BUG: Fix style.background_gradient() for nullable dtype (ex: Int64) series with pd.NA values
- [x] closes #50712
- [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.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

@attack68 Ok cool, I just re-merged master so hopefully it all works this time. If you look at one of the previous test runs, everything looks ok minus one windows test that seems somewhat flaky

![image](https://user-images.githubusercontent.com/2521996/212335587-510bf4ba-cdc9-4f7c-9115-f68401dddd5b.png)

Since then all I have done is re-merge master All comments addressed. 

@mroeschke @attack68 Thanks for the review Thanks @dhendry 