Retain Python version 3.11

since that is in Pipfile.

Author: HannoSpreeuw

.github/workflows/docs.yml

@@ -21,7 +21,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.12'
+          python-version: '3.11'
 
       # install all dependencies (including pdoc)
       - run: pip install pipenv