Update page.yaml to be python=3.9.7

.github/workflows/page.yaml

@@ -17,7 +17,7 @@ jobs:
       - name: Set up python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.8'
+          python-version: '3.9.7'
       - name: Set up dependencies
         run: pip install --quiet .
       - name: Compile sphinx