BUG: Fix droped result column in groupby with as_index False
- [x] closes #32240
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

The aggregate function *lost* the results of the aggregate operation, if the ```as_index=False``` flag was set and one of the result columns is relabeled. The index was reset at first, adding columns to the DataFrame. The relabeling operation only took the columns before resetting the index as input. So the weird error occurred. I changed the order of the index reset and the relabeling. This fixes the issue.
One comment otherwise LGTM Done @mroeschke  Merge conflict in whats new. Looks good. Looks like there are some failing code checks > 
> 
> Looks good. Looks like there are some failing code checks

Missed that one, is green now. let's rebase this on top of #34012 (or could wait, likey to merge that one tomorrow). this migth be fine but will want to re-look. @jreback Merged master after the other pull request was merged. Seems to be fine. @jreback  merged master @jreback Changed the docs, test failure seems unrelated looks good, can you rebase to fix the conflict (the other fail is ok), ping when ready. @jreback fixed conflict, failure unrelated. Can be merged can you merge master and ping when green @phofl if you can merge master will have another look Sorry, was a Bit busy the last few days. Will merge master tomorrow and ping when ready  thanks @phofl 