DEPR: Enforce numeric_only=False in groupby sum/mean
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Targeting these two ops first because they're used as an example op in a lot of tests. Hoping the rest of the ops are easier. Note this doesn't check off the corresponding line in the list of deprecations.
is the failed asv time_pivot_table_margins_only_column a false-positive? Thanks @jbrockmendel - ASV failure was due to trying to take the mean of a string column; I added it to the `columns` instead. It now takes 30ms on my machine.