PytestUnknownMarkWarning in tests

[mslw]

I am seeing the following warning when running tests:

../../../.virtualenvs/dl-redcap/lib/python3.9/site-packages/datalad/tests/utils_pytest.py:69
  /home/mszczepanik/.virtualenvs/dl-redcap/lib/python3.9/site-packages/datalad/tests/utils_pytest.py:69: PytestUnknownMarkWarning: Unknown pytest.mark.skip_if_on_windows - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/how-to/mark.html
    return getattr(pytest.mark, name)

Seems to be coming from DataLad core -- or is it a misconfiguration issue in the extension? Does anyone know?

It doesn't seem to cause any problems, but is annoying (another warning shown is a deprecation warning from boto, also in core, but this will hopefully be addressed in 0.19).

Using DataLad 0.18.2