Fix docs-html "cannot import name 'Callable' from 'collections'"

ImportError: cannot import name 'Callable' from 'collections'
(/opt/hostedtoolcache/Python/3.11.6/x64/lib/python3.11/collections/__init__.py)

.github/workflows/test.yaml

@@ -77,7 +77,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.x'
+          python-version: '3.9'
       - name: Install tox
         run: pip install tox
       - name: Run ${{ matrix.tox-env }}