tests: update pytest workflow

This sets the `PYTHONPATH` environment variable so we can run pytest
with the recent module refactor (module_utils introduction)

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>

.github/workflows/pytest.yml

@@ -22,3 +22,5 @@ jobs:
           architecture: x64
       - run: pip install -r tests/requirements.txt
       - run: pytest --cov=library/ --cov=plugins/filter/ -vvvv tests/library/ tests/plugins/filter/
+        env:
+          PYTHONPATH: "$PYTHONPATH:/home/runner/work/ceph-ansible/ceph-ansible/library:/home/runner/work/ceph-ansible/ceph-ansible/module_utils:/home/runner/work/ceph-ansible/ceph-ansible"