Add explicit pytest runner

.github/workflows/tests.yml

@@ -51,7 +51,7 @@ jobs:
       - name: Install dependencies
         run: |
              python -m pip install --upgrade pip
-             pip install -Ur 'requirements/*.txt'
+             pip install -Ur './requirements/requirements.txt'
       - name: Run pytest
         run: |
              cd tests && pytest test_*.py