CLN: use `lib.no_default` instead of `lib.NoDefault` in `.pivot`
- [x] Closes #53826
- [x] *No additional tests needed, it suffices to require all existing tests to pass*
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit)
- [x] *I assume that this does not need a changelog entry*

Nice one thanks @Charlie-XIAO (if you can think of a linting check to ensure `lib.NoDefault` is only used for typing, that would be a bonus)