Add workaround for GHA failur in 'macos-latest' with 3.9

Author: abravalheri

Diff for: .github/workflows/main.yml

@@ -63,9 +63,6 @@ jobs:
         - platform: ubuntu-latest
           python: "3.10"
           distutils: stdlib
-        # TODO: Re-evaluate the need for the following workaround
-        exclude:
-        - {python: "3.9", platform: "macos-latest"}  # actions/setup-python#981
     runs-on: ${{ matrix.platform }}
     continue-on-error: ${{ matrix.python == '3.14' }}
     env:
@@ -79,6 +76,9 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
           allow-prereleases: true
+        env:
+          # Workaround for actions/setup-python#981 (env var only modified for this specific step)
+          SETUPTOOLS_USE_DISTUTILS: ${{ matrix.platform == 'macos-latest' && matrix.python == '3.9' && 'stdlib' || matrix.distutils || 'local' }}
       - uses: actions/cache@v4
         id: cache
         with: