Drop regression_suite install from setup_venv.py. (#18072)

Progress on https://github.com/iree-org/iree/issues/16203.

We only run tests from
https://github.com/iree-org/iree/tree/main/experimental/regression_suite
in a few jobs, but other jobs are sharing this
`build_tools/pkgci/setup_venv.py` script, so this moves the extra
install closer to where it is needed.

Also drop the seemingly unused `IREERS_ARTIFACT_DIR` environment
variable that got copy/pasted around.
diff --git a/.github/workflows/pkgci_regression_test.yml b/.github/workflows/pkgci_regression_test.yml
index e21c447..4063721 100644
--- a/.github/workflows/pkgci_regression_test.yml
+++ b/.github/workflows/pkgci_regression_test.yml
@@ -62,7 +62,6 @@
               - os-family=Linux
     env:
       PACKAGE_DOWNLOAD_DIR: ${{ github.workspace }}/.packages
-      IREERS_ARTIFACT_DIR: ${{ github.workspace }}/artifacts
       CONFIG_FILE_PATH: build_tools/pkgci/external_test_suite/${{ matrix.config-file }}
       NUMPROCESSES: ${{ matrix.numprocesses }}
       LOG_FILE_PATH: /tmp/iree_tests_onnx_${{ matrix.name }}_logs.json
@@ -166,7 +165,6 @@
           # (note: would need to plumb the presubmit/postsubmit runner-group through to here too)
     env:
       PACKAGE_DOWNLOAD_DIR: ${{ github.workspace }}/.packages
-      IREERS_ARTIFACT_DIR: ${{ github.workspace }}/artifacts
       IREE_TEST_FILES: ${{ matrix.iree-tests-cache }}
       IREE_TEST_PATH_EXTENSION: ${{ github.workspace }}/build_tools/pkgci/external_test_suite
       MODELS_CONFIG_FILE_PATH: build_tools/pkgci/external_test_suite/${{ matrix.models-config-file }}
@@ -263,7 +261,6 @@
             runs-on: nodai-amdgpu-mi300-x86-64
     env:
       PACKAGE_DOWNLOAD_DIR: ${{ github.workspace }}/.packages
-      IREERS_ARTIFACT_DIR: ${{ github.workspace }}/artifacts
       IREE_TEST_FILES: ${{ matrix.iree-tests-cache }}
       IREE_TEST_PATH_EXTENSION: ${{ github.workspace }}/build_tools/pkgci/external_test_suite
       VENV_DIR: ${{ github.workspace }}/venv
@@ -292,6 +289,8 @@
           ./build_tools/pkgci/setup_venv.py ${VENV_DIR} \
             --artifact-path=${PACKAGE_DOWNLOAD_DIR} \
             --fetch-gh-workflow=${{ inputs.artifact_run_id }}
+          source ${VENV_DIR}/bin/activate
+          pip install -e experimental/regression_suite
 
       # TODO(#17344): regenerate .mlirbc files, test plat_rdna3_rocm on rocm
       # # In-tree tests
diff --git a/.github/workflows/pkgci_test_tensorflow_cpu.yml b/.github/workflows/pkgci_test_tensorflow_cpu.yml
index 09cfea6..221274a 100644
--- a/.github/workflows/pkgci_test_tensorflow_cpu.yml
+++ b/.github/workflows/pkgci_test_tensorflow_cpu.yml
@@ -23,7 +23,6 @@
     runs-on: ubuntu-20.04
     env:
       PACKAGE_DOWNLOAD_DIR: ${{ github.workspace }}/.packages
-      IREERS_ARTIFACT_DIR: ${{ github.workspace }}/artifacts
       VENV_DIR: ${{ github.workspace }}/.venv
       IREE_VMVX_DISABLE: 0
     steps:
diff --git a/.github/workflows/pkgci_unit_test.yml b/.github/workflows/pkgci_unit_test.yml
index 138043a..27ed919 100644
--- a/.github/workflows/pkgci_unit_test.yml
+++ b/.github/workflows/pkgci_unit_test.yml
@@ -42,6 +42,8 @@
           ./build_tools/pkgci/setup_venv.py ${VENV_DIR} \
             --artifact-path=${PACKAGE_DOWNLOAD_DIR} \
             --fetch-gh-workflow=${{ inputs.artifact_run_id }}
+          source ${VENV_DIR}/bin/activate
+          pip install -r runtime/bindings/python/iree/runtime/build_requirements.txt
       - name: Validate runtime wheel
         run: |
           source ${VENV_DIR}/bin/activate
diff --git a/build_tools/pkgci/setup_venv.py b/build_tools/pkgci/setup_venv.py
index 362627a..618bb37 100755
--- a/build_tools/pkgci/setup_venv.py
+++ b/build_tools/pkgci/setup_venv.py
@@ -26,7 +26,6 @@
 import functools
 from glob import glob
 import json
-import os
 import sys
 from pathlib import Path
 import platform
@@ -118,16 +117,6 @@
             args.artifact_path = td
             return main(args)
 
-    # Find the regression suite project.
-    rs_dir = (
-        (Path(__file__).resolve().parent.parent.parent)
-        / "experimental"
-        / "regression_suite"
-    )
-    if not rs_dir.exists():
-        print(f"Could not find regression_suite project: {rs_dir}")
-        return 1
-
     artifact_prefix = f"{platform.system().lower()}_{platform.machine()}"
     wheels = []
     for package_stem, variant in [
@@ -169,21 +158,6 @@
         print(f"Running command: {' '.join([str(c) for c in cmd])}")
         subprocess.check_call(cmd)
 
-    # Now install the regression suite project, which will bring in any deps.
-    cmd = [
-        str(python_exe),
-        "-m",
-        "pip",
-        "install",
-        "--force-reinstall",
-        "--timeout",
-        "60",
-        "-e",
-        str(rs_dir) + os.sep,
-    ]
-    print(f"Running command: {' '.join(cmd)}")
-    subprocess.check_call(cmd)
-
     return 0
 
 
diff --git a/experimental/regression_suite/README.md b/experimental/regression_suite/README.md
index 53668b3..7665c5a 100644
--- a/experimental/regression_suite/README.md
+++ b/experimental/regression_suite/README.md
@@ -9,7 +9,7 @@
 
 If you have IREE tools on your path or have a virtual environment setup:
 
-```
+```bash
 pip install -e experimental/regression_suite
 PATH=../iree-build/tools:$PATH \
 pytest experimental/regression_suite
@@ -39,13 +39,16 @@
 GitHub presubmit or postsubmit run. This can be done in one step by setting
 up a venv:
 
-```
+```bash
 deactivate  # If have any venv active.
 python ./build_tools/pkgci/setup_venv.py \
   /tmp/iree_gh_venv \
-  --fetch-gh-workflow=<<RUN_ID>> \
+  --fetch-gh-workflow=${RUN_ID} \
   [--compiler-variant=asserts] [--runtime-variant=asserts]
 source /tmp/iree_gh_venv/bin/activate
+
+# Then install the regression suite and run pytest as usual:
+pip install -e experimental/regression_suite
 ```
 
 In the above, `<<RUN_ID>>` is the value in any GitHub action presubmit/postsubmit
diff --git a/integrations/tensorflow/test/requirements.txt b/integrations/tensorflow/test/requirements.txt
index 69c8ae3..c7a6fb5 100644
--- a/integrations/tensorflow/test/requirements.txt
+++ b/integrations/tensorflow/test/requirements.txt
@@ -2,3 +2,4 @@
 tensorflow>=2.16.1
 keras>=2.7.0
 Pillow>=9.2.0
+pytest