ci: timeout tests if it takes >5min

It most likely means it's frozen and unlikely to resume again. We'd want
to see where it froze, so this will provide us with a traceback.

.github/workflows/tests.yaml

@@ -69,8 +69,11 @@ jobs:
         pip install --upgrade pip wheel
         pip install -e ".[dev]"
     - name: run tests
-      timeout-minutes: 20
-      run: pytest -nauto --durations 100 --cov --cov-report=xml --cov-report=term -k "${{ matrix.pytest-filter }}"
+      timeout-minutes: 30
+      run: >
+        pytest -nauto --timeout=300 --durations=100
+        --cov --cov-report=xml --cov-report=term
+        -k "${{ matrix.pytest-filter }}"
     - name: upload coverage report
       uses: codecov/codecov-action@v3
       with: