Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/docs/dev/reference/api/pandas.core.groupby.SeriesGroupBy.hist.html (and other places)

Documentation problem

AxesSubplot was removed from matplotlib, so we need to remove it from our docs.

See matplotlib/matplotlib#18222

Suggested fix for documentation

Change the type from AxesSubplot in the docs to Axes