ci: use python 3.12 venv for test-kernels install step

The Strix Halo runner uses a custom container-hook that exec's commands
with a PATH where /usr/bin/python3 (Debian 3.11, PEP 668 externally
managed) precedes /usr/local/bin/python3 (3.12). uv pip install --system
then fails with 'externally managed' against the system 3.11.

Create a venv from /usr/local/bin/python3.12 instead and prepend its
bin/ to GITHUB_PATH so subsequent python and pytest invocations resolve
to the venv interpreter.

Signed-off-by: Matthias Gehre <matthias.gehre@amd.com>

Author: mgehre-amd

.github/workflows/build-rocm-wheels.yml

@@ -189,21 +189,27 @@ jobs:
 
       - name: Install wheel and test dependencies
         run: |
+          # Create a venv with Python 3.12 from the CI image. The runner's
+          # exec PATH may put Debian's PEP 668-marked /usr/bin/python3.11
+          # first, which breaks `uv pip install --system`.
+          uv venv --python 3.12 "$GITHUB_WORKSPACE/.venv"
+          echo "$GITHUB_WORKSPACE/.venv/bin" >> "$GITHUB_PATH"
+          source "$GITHUB_WORKSPACE/.venv/bin/activate"
           # Pin torch from the nightly ROCm index *only* (no PyPI
           # fallback) so we always get the ROCm wheel.
-          uv pip install --system \
+          uv pip install \
             --upgrade-package torch \
             torch \
             --index-url ${{ env.PYTORCH_INDEX_URL }}
-          uv pip install --system dist/*.whl \
+          uv pip install dist/*.whl \
             pytest pytest-timeout numpy \
             tblib transformers huggingface_hub sentencepiece pillow \
             --index-url ${{ env.PYTORCH_INDEX_URL }} \
             --extra-index-url https://pypi.org/simple/ \
             --index-strategy unsafe-first-match
           # Nightly torchvision has operator ABI mismatch with nightly torch.
           # Our kernel tests don't need it; remove to prevent conftest crash.
-          uv pip uninstall --system torchvision 2>/dev/null || true
+          uv pip uninstall torchvision 2>/dev/null || true
 
       - name: Prepare test environment
         run: |