Update iree test cache location for new mi250 cluster (#18083)

As we move to using the Alpha 2 mi250 cluster, each home directory only
has 100GB available to it. There is a shared storage for each group (our
being aig_sharks) where we get access to 10 TB. So, this is updating the
cache location to use that. Previously when using home directory, the
100gb got filled up and CI went down for the mi250 last night.

.github/workflows/pkgci_regression_test.yml

diff --git a/.github/workflows/pkgci_regression_test.yml b/.github/workflows/pkgci_regression_test.yml
index d2d7c0f..e21c447 100644
--- a/.github/workflows/pkgci_regression_test.yml
+++ b/.github/workflows/pkgci_regression_test.yml
@@ -139,17 +139,21 @@
           # CPU
           - name: cpu_llvm_task
             models-config-file: models_cpu_llvm_task.json
+            iree-tests-cache: ~/iree_tests_cache
             runs-on: nodai-amdgpu-w7900-x86-64
 
           # AMD GPU
           - name: amdgpu_rocm_mi250_gfx90a
             models-config-file: models_gpu_rocm_gfx90a.json
+            iree-tests-cache: /groups/aig_sharks/iree-tests-cache
             runs-on: nodai-amdgpu-mi250-x86-64
           - name: amdgpu_rocm_mi300_gfx942
             models-config-file: models_gpu_rocm_gfx942.json
+            iree-tests-cache: ~/iree_tests_cache
             runs-on: nodai-amdgpu-mi300-x86-64
           - name: amdgpu_vulkan
             models-config-file: models_gpu_vulkan.json
+            iree-tests-cache: ~/iree_tests_cache
             runs-on: nodai-amdgpu-w7900-x86-64
 
           # NVIDIA GPU
@@ -163,7 +167,7 @@
     env:
       PACKAGE_DOWNLOAD_DIR: ${{ github.workspace }}/.packages
       IREERS_ARTIFACT_DIR: ${{ github.workspace }}/artifacts
-      IREE_TEST_FILES: ~/iree_tests_cache
+      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 }}
       VENV_DIR: ${{ github.workspace }}/venv
@@ -243,21 +247,24 @@
           - name: cpu_llvm_task
             models-config-file: models_cpu_llvm_task.json
             backend: cpu
+            iree-tests-cache: ~/iree_tests_cache
             runs-on: nodai-amdgpu-w7900-x86-64
 
           # AMD GPU
           - name: amdgpu_rocm_mi250_gfx90a
             rocm-chip: gfx90a
             backend: rocm
+            iree-tests-cache: /groups/aig_sharks/iree-tests-cache
             runs-on: nodai-amdgpu-mi250-x86-64
           - name: amdgpu_rocm_mi300_gfx942
             rocm-chip: gfx942
             backend: rocm
+            iree-tests-cache: ~/iree_tests_cache
             runs-on: nodai-amdgpu-mi300-x86-64
     env:
       PACKAGE_DOWNLOAD_DIR: ${{ github.workspace }}/.packages
       IREERS_ARTIFACT_DIR: ${{ github.workspace }}/artifacts
-      IREE_TEST_FILES: ~/iree_tests_cache
+      IREE_TEST_FILES: ${{ matrix.iree-tests-cache }}
       IREE_TEST_PATH_EXTENSION: ${{ github.workspace }}/build_tools/pkgci/external_test_suite
       VENV_DIR: ${{ github.workspace }}/venv
       LD_LIBRARY_PATH: /home/esaimana/Python-3.11.9