update to python 3.9

Author: isabelizimm

.github/workflows/docs.yml

@@ -18,7 +18,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-python@v4
         with:
-          python-version: 3.8
+          python-version: 3.9
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip