STYLE: Inconsistent namespace - apply (pandas-dev#39992)
Fix inconsistent namespace in apply directory.

- [x] xref #39992
- [ ] 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
- [ ] whatsnew entry

@MarcoGorelli  Sure. I have reverted it back. Thanks for guiding me. Hope this looks fine now. > Hope this looks fine now.

You still need to fixup the error from the `black` formatter

```
pre-commit run --files pandas/tests/apply/test_frame_apply.py pandas/tests/apply/test_series_apply.py
```

---

Or just comment `@github-actions pre-commit` and that'll trigger a workflow which'll fix it up for you Done. @MarcoGorelli go ahead and merge PRs like this that are all green-ish sure, thanks - flake8 and the rest pass, so this should be good to go