CI: Doc build failing

```
/home/vsts/work/1/s/pandas/core/indexes/multi.py:docstring of pandas.MultiIndex.rst:91: WARNING: autosummary: stub file not found 'pandas.MultiIndex.get_locs'. Check your autosummary_generate setting.
looking for now-outdated files... none found
```

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=23019