Replace old string formatting syntax with f-strings #29547
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @ynorouzz! Thanks for opening this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:

* In the file [`pandas/tests/series/indexing/test_where.py`](https://github.com/pandas-dev/pandas/blob/f993356973fcd24cdfa6934c6baef36fd2ff7a21/pandas/tests/series/indexing/test_where.py):

> [Line 226:89](https://github.com/pandas-dev/pandas/blob/f993356973fcd24cdfa6934c6baef36fd2ff7a21/pandas/tests/series/indexing/test_where.py#L226): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (92 > 88 characters)

 there are some linting issues see https://github.com/pandas-dev/pandas/pull/34903/checks?check_run_id=790893140 @ynorouzz is this still active? Can you address the comments / failures? closing since these were changed to f-strings in #34502 which has been merged, hence the conflict.