Disable external test suite on ROCm while flaky. (#16705)

Seeing flaky failures in different tests each time, like these:

*
https://github.com/openxla/iree/actions/runs/8195423846/job/22413939662#step:9:47
*
https://github.com/openxla/iree/actions/runs/8195232491/job/22413293699?pr=16703#step:9:47
*
https://github.com/openxla/iree/actions/runs/8196441429/job/22416930820?pr=16704#step:9:47

Reducing parallelism helped with somewhat similar errors before, but I
suspect there are some real issues in either the compiler, runtime, ROCm
driver, or runner machine. Probably need to debug the code/machine more
directly.
diff --git a/.github/workflows/pkgci_regression_test_amdgpu_rocm.yml b/.github/workflows/pkgci_regression_test_amdgpu_rocm.yml
index 729b2e4..44de820 100644
--- a/.github/workflows/pkgci_regression_test_amdgpu_rocm.yml
+++ b/.github/workflows/pkgci_regression_test_amdgpu_rocm.yml
@@ -53,22 +53,24 @@
             -rA -s -m "plat_rdna3_rocm and presubmit" \
             experimental/regression_suite
 
-      # Out of tree tests
-      - name: Checking out external TestSuite repository
-        uses: actions/checkout@8f4b7f84864484a7bf31766abe9204da3cbe65b3 # v3.5.0
-        with:
-          repository: nod-ai/SHARK-TestSuite
-          ref: 00053290a576ae39aecb6fb2757b58fcd3b143f2
-          path: SHARK-TestSuite
-          submodules: false
-      - name: Installing external TestSuite Python requirements
-        run: |
-          source ${VENV_DIR}/bin/activate
-          python -m pip install -r SHARK-TestSuite/iree_tests/requirements.txt
-      - name: Run external TestSuite tests
-        env:
-          IREE_TEST_CONFIG_FILES: experimental/regression_suite/external_test_suite/config_gpu_rocm_rdna3.json
-        run: |
-          source ${VENV_DIR}/bin/activate
-          export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/rocm/lib:/opt/rocm/hip/lib
-          pytest SHARK-TestSuite/iree_tests -n 4 -rpfE --timeout=60
+      # Disabled while flaky. Might be replaced with HIP tests instead?
+
+      # # Out of tree tests
+      # - name: Checking out external TestSuite repository
+      #   uses: actions/checkout@8f4b7f84864484a7bf31766abe9204da3cbe65b3 # v3.5.0
+      #   with:
+      #     repository: nod-ai/SHARK-TestSuite
+      #     ref: 00053290a576ae39aecb6fb2757b58fcd3b143f2
+      #     path: SHARK-TestSuite
+      #     submodules: false
+      # - name: Installing external TestSuite Python requirements
+      #   run: |
+      #     source ${VENV_DIR}/bin/activate
+      #     python -m pip install -r SHARK-TestSuite/iree_tests/requirements.txt
+      # - name: Run external TestSuite tests
+      #   env:
+      #     IREE_TEST_CONFIG_FILES: experimental/regression_suite/external_test_suite/config_gpu_rocm_rdna3.json
+      #   run: |
+      #     source ${VENV_DIR}/bin/activate
+      #     export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/rocm/lib:/opt/rocm/hip/lib
+      #     pytest SHARK-TestSuite/iree_tests -n 4 -rpfE --timeout=60