Remove Python 3.7 and test Django 4.0

Author: davegaeddert

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10"]
+        python-version: ["3.8", "3.9", "3.10"]
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2