Run tests relying only on git fixtures

.github/workflows/tests.yml

@@ -34,6 +34,4 @@ jobs:
           python -m pip install -r requirements.txt
           python setup.py install
       - name: Run tests for ${{ matrix.python-version }}
-        run: |
-          git branch -m main  # still master by default in GitHub Actions
-          pytest -vvv
+        run: pytest -vvv