BUG: fallback from issue 20824 no longer occurs due to skipna flag
- [ ] closes #20824
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Issue #20824 found that a fallback was occuring when df.Groupby().sum() was called with the skipna flag. This was occurring because the _cython_agg_general function was not accepting the argument, which has now been fixed. The fallback still occurs with strings in the df, however this is a deeper issue stemming from the _aggregate() call in groupby/ops.py (line 572).
