Fix failure to use autoclass on non-traitlets configurable classes

[blink1073]

Seen while working on jupyter/nbclient#230:

reading sources... [100%] reference/nbclient.tests
Exception occurred:
  File "/Users/silvester/miniconda/envs/nbclient_env/lib/python3.10/site-packages/autodoc_traits/autodoc_traits.py", line 20, in get_object_members
    else self.object.class_traits
AttributeError: type object 'NBClientTestsBase' has no attribute 'class_traits'

[welcome]

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[consideRatio]

Thanks @blink1073, makes sense to me!

I understand it as the bug will show up if you use the autoclass directive (or the automodule directive) on classes that isn't coupled to traitlets in any way.

[blink1073]

Yes, using automodule with a mix of traitlets and non-traitlets classes triggered the error.