Update python-app.yml

.github/workflows/python-app.yml

@@ -20,6 +20,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
+        python -m pip install --quiet --ignore-installed sphinx==3.2.1
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: Execute python
       run: |