BUG: startswith function gives misleading results when passed a series #3485

- [x] closes #3485
- [] tests added / passed
- [x] 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
``` python import pandas
d = pandas.DataFrame([['hi,hi 2'],['bye','bye 2']], columns=['one','two'])
print(d.one.str.startswith(d.two))
```
Hello @oraby8! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-10-10 09:40:33 UTC 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. this needs tests if you would like to continue working pls ping.