Use Python 3.8 for now

Author: methane

Diff for: .github/workflows/django.yaml

@@ -23,7 +23,8 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: "3.9"
+          # https://www.mail-archive.com/[email protected]/msg209056.html
+          python-version: "3.8"
 
       - uses: actions/checkout@v2
         with: