CI: Drop 3.7 tests

Author: effigies

.github/workflows/unittests.yml

@@ -34,7 +34,7 @@ jobs:
     strategy:
       max-parallel: 5
       matrix:
-        python-version: [3.7, 3.8, 3.9]
+        python-version: [3.8, 3.9]
 
     steps:
     - uses: actions/cache@v3