BUG: parsing pyarrow dtypes corner case
- [x] closes #51225 (Replace xxxx with the GitHub issue number)
- [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
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

pretty dumb corner case
release note? I think also should now target 2.1 now that rc is cut as this is not a 2.0.x regression or bugfix for a new feature. Arrow support is more or less new, I think we can backport relevant fixes there wasn't pd.ArrowDtype was added in 1.5? Yes, but support was very limited for arrow stuff in 1.5 sure. it is experimental and this is not a big change so no objections to targeting 2.0 thx @jbrockmendel 