test using xdist for faster tests

.github/workflows/pytest.yml

@@ -136,7 +136,11 @@ jobs:
 
       - name: Test with pytest
         run: |
-          python3 -m pytest tests/${{matrix.test}} --color=yes --cov --durations=0 && exit_code=0|| exit_code=$?
+          # run in parallel with xdist if not test_modules.py or test_subworkflows.py
+          if [ "${{ matrix.test }}" != "test_modules.py" ] && [ "${{ matrix.test }}" != "test_subworkflows.py" ]; then
+            python3 -m pytest tests/${{matrix.test}} --color=yes --cov --durations=0 -n 2 && exit_code=0|| exit_code=$?
+          else
+            python3 -m pytest tests/${{matrix.test}} --color=yes --cov --durations=0 && exit_code=0|| exit_code=$?
           # don't fail if no tests were collected, e.g. for test_licence.py
           if [ "${exit_code}" -eq 5 ]; then
             echo "No tests were collected"