[CI] Split the welcome message workflow for issue/PR (#24705)

The initial implementation in commit ff836d7 causes both issue-greeter
and pull-request-greeter steps to be attempted [0] on both PRs and
issues. Avoid the confusion by splitting into dedicated workflows and
retiring the initial "GitHub Automation".

[0] https://github.com/iree-org/iree/actions/runs/29332508441

Signed-off-by: Artem Gindinson <gindinson@roofline.ai>
diff --git a/.github/workflows/github_automation.yml b/.github/workflows/github_automation.yml
deleted file mode 100644
index 1e06dc4..0000000
--- a/.github/workflows/github_automation.yml
+++ /dev/null
@@ -1,89 +0,0 @@
-# Copyright 2026 The IREE Authors
-#
-# Licensed under the Apache License v2.0 with LLVM Exceptions.
-# See https://llvm.org/LICENSE.txt for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-name: GitHub Automation
-
-on:
-  issues:
-    types:
-      - opened
-  pull_request_target:
-    types:
-      - opened
-
-permissions:
-  contents: read
-
-jobs:
-  pr-greeter:
-    runs-on: ubuntu-24.04
-    permissions:
-      contents: read
-      pull-requests: write
-    # Only comment on PRs opened by someone new to IREE or to GitHub as a whole.
-    if: >-
-      github.repository == 'iree-org/iree' &&
-      github.event_name == 'pull_request_target' &&
-      github.event.pull_request.author_association != 'COLLABORATOR' &&
-      github.event.pull_request.author_association != 'CONTRIBUTOR' &&
-      github.event.pull_request.author_association != 'MANNEQUIN' &&
-      github.event.pull_request.author_association != 'MEMBER' &&
-      github.event.pull_request.author_association != 'OWNER'
-    steps:
-      - name: Checking out repository
-        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
-        with:
-          persist-credentials: false
-      - name: Setting up Python
-        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
-      - name: Installing dependencies
-        run: python -m pip install --disable-pip-version-check PyGithub==2.4.0
-      - name: Greet first-time contributor
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          ISSUE_NUMBER: ${{ github.event.pull_request.number }}
-          PR_AUTHOR: ${{ github.event.pull_request.user.login }}
-        run: |
-          python ./build_tools/github_actions/github_automation.py \
-            --token "$GH_TOKEN" \
-            pr-greeter \
-            --issue-number "$ISSUE_NUMBER" \
-            --author "$PR_AUTHOR"
-
-  issue-greeter:
-    runs-on: ubuntu-24.04
-    permissions:
-      contents: read
-      issues: write
-    # Only comment on issues opened by someone new to IREE or to GitHub as a whole.
-    if: >-
-      github.repository == 'iree-org/iree' &&
-      github.event_name == 'issues' &&
-      github.event.issue.author_association != 'COLLABORATOR' &&
-      github.event.issue.author_association != 'CONTRIBUTOR' &&
-      github.event.issue.author_association != 'MANNEQUIN' &&
-      github.event.issue.author_association != 'MEMBER' &&
-      github.event.issue.author_association != 'OWNER'
-    steps:
-      - name: Checking out repository
-        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
-        with:
-          persist-credentials: false
-      - name: Setting up Python
-        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
-      - name: Installing dependencies
-        run: python -m pip install --disable-pip-version-check PyGithub==2.4.0
-      - name: Greet first-time contributor
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          ISSUE_NUMBER: ${{ github.event.issue.number }}
-          ISSUE_AUTHOR: ${{ github.event.issue.user.login }}
-        run: |
-          python ./build_tools/github_actions/github_automation.py \
-            --token "$GH_TOKEN" \
-            issue-greeter \
-            --issue-number "$ISSUE_NUMBER" \
-            --author "$ISSUE_AUTHOR"
diff --git a/.github/workflows/issue_greeter.yml b/.github/workflows/issue_greeter.yml
new file mode 100644
index 0000000..00fe838
--- /dev/null
+++ b/.github/workflows/issue_greeter.yml
@@ -0,0 +1,50 @@
+# Copyright 2026 The IREE Authors
+#
+# Licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+name: Issue Greeter
+
+on:
+  issues:
+    types:
+      - opened
+
+permissions:
+  contents: read
+
+jobs:
+  issue-greeter:
+    runs-on: ubuntu-24.04
+    permissions:
+      contents: read
+      issues: write
+    # Only comment on issues opened by someone new to IREE or to GitHub as a whole.
+    if: >-
+      github.repository == 'iree-org/iree' &&
+      github.event.issue.author_association != 'COLLABORATOR' &&
+      github.event.issue.author_association != 'CONTRIBUTOR' &&
+      github.event.issue.author_association != 'MANNEQUIN' &&
+      github.event.issue.author_association != 'MEMBER' &&
+      github.event.issue.author_association != 'OWNER'
+    steps:
+      - name: Checking out repository
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          persist-credentials: false
+      - name: Setting up Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+      - name: Installing dependencies
+        run: python -m pip install --disable-pip-version-check PyGithub==2.4.0
+      - name: Greet first-time contributor
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE_NUMBER: ${{ github.event.issue.number }}
+          ISSUE_AUTHOR: ${{ github.event.issue.user.login }}
+        run: |
+          python ./build_tools/github_actions/github_automation.py \
+            --token "$GH_TOKEN" \
+            issue-greeter \
+            --issue-number "$ISSUE_NUMBER" \
+            --author "$ISSUE_AUTHOR"
diff --git a/.github/workflows/pull_request_greeter.yml b/.github/workflows/pull_request_greeter.yml
new file mode 100644
index 0000000..1751853
--- /dev/null
+++ b/.github/workflows/pull_request_greeter.yml
@@ -0,0 +1,50 @@
+# Copyright 2026 The IREE Authors
+#
+# Licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+name: Pull Request Greeter
+
+on:
+  pull_request_target:
+    types:
+      - opened
+
+permissions:
+  contents: read
+
+jobs:
+  pr-greeter:
+    runs-on: ubuntu-24.04
+    permissions:
+      contents: read
+      pull-requests: write
+    # Only comment on PRs opened by someone new to IREE or to GitHub as a whole.
+    if: >-
+      github.repository == 'iree-org/iree' &&
+      github.event.pull_request.author_association != 'COLLABORATOR' &&
+      github.event.pull_request.author_association != 'CONTRIBUTOR' &&
+      github.event.pull_request.author_association != 'MANNEQUIN' &&
+      github.event.pull_request.author_association != 'MEMBER' &&
+      github.event.pull_request.author_association != 'OWNER'
+    steps:
+      - name: Checking out repository
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          persist-credentials: false
+      - name: Setting up Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+      - name: Installing dependencies
+        run: python -m pip install --disable-pip-version-check PyGithub==2.4.0
+      - name: Greet first-time contributor
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE_NUMBER: ${{ github.event.pull_request.number }}
+          PR_AUTHOR: ${{ github.event.pull_request.user.login }}
+        run: |
+          python ./build_tools/github_actions/github_automation.py \
+            --token "$GH_TOKEN" \
+            pr-greeter \
+            --issue-number "$ISSUE_NUMBER" \
+            --author "$PR_AUTHOR"