Update tests.yml

Author: MarcoMuellner

.github/workflows/tests.yml

@@ -20,7 +20,7 @@ jobs:
       - run: pip install poetry==1.1.13
       - run: poetry install
       - run: poetry run pytest
-      - run: poetry run pytest --cov=src/ --cov-report=xml        
+      - run: poetry run pytest --cov=src/ --cov-report=xml --cov-fail-under 90       
       - uses: codecov/codecov-action@v2
         if: always()
         with: