Many warnings like: Unknown pytest.mark.auth - is this a typo? due to unregistered custom pytest marks.

[captainkirk99]

We have many warnings like this:

src/pydap/tests/test_cas_esgf.py:16
  /home/ed/p1/src/pydap/tests/test_cas_esgf.py:16: PytestUnknownMarkWarning: Unknown pytest.mark.auth - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/mark.html
    @pytest.mark.auth

These are easy to fix by registering our custom marks...