DEPR: indexing Series with single-entry list
- [x] closes #31299 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Could use a better warning message, suggestions welcome.
> Will users see this warning in addition to the warnings in #31299 (comment)?

No, this will change the list to tuple before calling `ndarray.__getitem__`

> Will need a whatsnew note.

updated thanks, can you add to the deprecation issue (do this for anything we are deprecating).