ci: update test workflow run command

Author: Apolo151

.github/workflows/pytest_coverage.yaml

@@ -26,4 +26,4 @@ jobs:
 
       - name: Run tests with coverage
         run: |
-          pytest --cov=. --cov-report=xml --cov-report=term
+          PYTHONPATH=. pytest --cov=. --cov-report=xml --cov-report=term