BUG: groupby.apply requires func to be hashable. raises unhashable type error otherwise about pandas

[rhshadrach]

Thanks for investigating @Aloqeely - #57444 is changing long standing intentional behavior, so must be done in a major release.

We could patch this by doing the lookup as a try-except, since anytime it would fail we would want to use the function as-is anyways. But because this isn't a regression, I think we should just wait until 3.0 resolves it.

[Aloqeely]

Thanks for the report! I am unable to reproduce this on main but I am able to reproduce on latest release 2.2.2
This seems to be caused by the following in pandas/core/groupby/groupby.py apply function:

orig_func = func
func = com.is_builtin_func(func)
if orig_func != func:
    alias = com._builtin_table_alias[orig_func]
    warn_alias_replacement(self, orig_func, alias)

Which internally was checking for whether or not the apply func you provided was deprecated or not by checking if it exists in the _builtin_table dictionary, and since dictionary keys must be hashable, _builtin_table.get(arg, arg) raised TypeError: unhashable type: 'Multiple'

I think this was fixed in #57444 which just enforced the deprecation and removed this check.
I would've called for a backport if this was fixed intentionally but I don't know what to do here. cc @rhshadrach