.github/workflows/macos.yml: Use tox via 'pipx run'

Author: Matthias Koeppe

.github/workflows/macos.yml

@@ -83,10 +83,16 @@ jobs:
           repository: ${{ inputs.sage_repo }}
           ref: ${{ inputs.sage_ref }}
           fetch-depth: 10000
-
+      - uses: actions/setup-python@v5
+        # As of 2024-02-03, the macOS M1 runners do not have preinstalled python or pipx.
+        # Installing pipx follows the approach of https://github.com/pypa/cibuildwheel/pull/1743
+        id: python
+        with:
+          python-version: "3.8 - 3.12"
+          update-environment: false
       - name: Install test prerequisites
         run: |
-          pipx install tox
+          "${{ steps.python.outputs.python-path }}" -m pip install pipx
       - name: Download upstream artifact
         uses: actions/download-artifact@v3
         with:
@@ -139,7 +145,7 @@ jobs:
                              ;;
           esac
           (sleep ${{ inputs.timeout }}; pkill make) &
-          MAKE="make -j12" tox -e $TOX_ENV -- SAGE_NUM_THREADS=6 $TARGETS
+          MAKE="make -j12" "${{ steps.python.outputs.python-path }}" -m pipx run tox -e $TOX_ENV -- SAGE_NUM_THREADS=6 $TARGETS
       - name: Prepare logs artifact
         run: |
           mkdir -p "artifacts/$LOGS_ARTIFACT_NAME"; cp -r .tox/*/log "artifacts/$LOGS_ARTIFACT_NAME"