DOC: Typo(s?) in pandas.DataFrame.isin
- [🗸] closes #43755 
- [🗸] tests added / passed
- [🗸] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [🗸] whatsnew entry

@jreback I did the changes you suggested, you can review them. thanks @Varun270 