new "unexpected warning" during sphinx build

[drammock]

This showed up in the CIs for #2717:

https://github.com/pydata/pydata-sphinx-theme/actions/runs/4796492713/jobs/8538010152

Unexpected warning: /opt/hostedtoolcache/Python/3.11.3/x64/lib/python3.11/site-packages/pandas/core/frame.py:docstring of pandas.core.frame.DataFrame.drop:1: WARNING: undefined label: 'advanced.shown_levels'

May need to add it to our list of expected warnings? Presumably caused by an upstream change in Pandas.

[12rambau]

should we fix pandas version instead ? (I never really dived in the documentation section but I assume freezeing the version should avoid these issues right ?

[drammock]

Personally I've never really liked the inclusion of pandas doc pages in our own docs. Given how widely used the theme is now (>6k users according to GitHub) I feel like we can trust that someone will tell us if things don't look good in their API docs. Also, we've recently made a few functions from our __init__.py public, which means we really ought to document those and include them in our online docs, which would provide a similar sort of test (smaller and probably less thorough, but IMO probably still good enough). WDYT?

[drammock]

for now though I think we should just add this warning to get CIs green again. I'll split out the question of keeping/removing pandas into a separate issue.