TST: add test to check numeric precision GH33234
test to check numeric precision after .groupby and .agg

- [X] closes #33234
- [X] tests added / passed
- [X] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [X] whatsnew entry

This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. Thanks for the PR, but it appears to have gone stale. If interested in continuing, please merge in master and address the comments and we can reopen. @mroeschke , can I continue the PR? I want to do some contribution. Sure, go for it