ci: Run pytest tests with debug logging

The logs won't be shown if the tests pass, but if they don't the
messages can be invaluable for debugging failures.

.github/workflows/main.yml

@@ -122,7 +122,7 @@ jobs:
 
       - name: Python tests
         run: |
-          pipenv run python -m pytest
+          pipenv run python -m pytest --log-level DEBUG
 
       - name: Build
         run: |