REGR: GH50127 fixes error for converting to / creating Index with dtype `S3`
- [x] closes #50127
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions. (Does not apply)
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

CI check error seems to be unrelated, since it appears on all latest CIs.

No error other than that, so happy to review it now ~moving off the 2.0 milestone as this is a regression from 1.5~

EDIT: sorry, this one worked on 1.5. Is it a blocker? Release day, moving this to the 2.1 milestone. Sorry, my bad, the next release should be 2.0.1, changed the milestone again. ` Ubuntu / Numpy Dev (pull_request)` is failing on all recent PRs, so I guess it is not related to the changes done here. Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen. this was close to ready, re-opening.  @Daquisu can you merge main and address any outstanding comments @Daquisu can you merge main and address any outstanding comments?  ill make reviewing this a priority Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.