feat(workflow): add pytest step after API readiness check

- Added a step in workflow to run tests using `pytest` after ensuring the backend service is ready.
- Tests are executed inside the running Docker container using `docker exec` to maintain consistency with the containerized environment.

.github/workflows/test-backend.yml

@@ -28,3 +28,8 @@ jobs:
             curl --silent --fail http://localhost:8000/health && break
             sleep 2
           done
+          echo "API is ready!"
+
+      - name: Run Tests with pytest
+        run: |
+          docker exec backend-container poetry run pytest --maxfail=3 --disable-warnings -v