tox
There is currently an error to debug with `test_tasks.py::test_lister`:
ERROR celery.app.trace:trace.py:254 Task swh.lister.pypi.tasks.PyPIListerTask[0ce5ba4b-8236-4fa1-ae07-0ad01cf34be8] raised unexpected: EncodeError(TypeError('Object of type MagicMock is not JSON serializable'))