Fix scatter norm keyword
- [x] closes #45809
- [ ] [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).
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

This PR addresses a bug where the `norm` parameter is used for a scatter plot where the `c` color is a non-categorical type (e.g. a numeric type). This combination of inputs would result in the `norm` parameter being specified both as an explicit keyword argument and in `self.kwds`.

The behavior has changed such that `norm` is only ever specified once, and in the scenario described above the value specified by the user will be honored.

I tried to test that the specific `norm` value ended up in the plot, but there doesn't seem to be a good way of comparing `norm._scale` objects without comparing the individual attributes. I'm happy to add this in if required.
small comment & if you can merge master; ping on green Great PR @Andy-Grigg, thanks.  sure can do another PR to update 