BUG: Fix passing `Colormap` instance to plot methods with mpl >= 3.6
- [x] closes #49374
- [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 an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Just a merge conflict, otherwise looks good Thanks for the quick fix @zmoon  Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
git checkout 1.5.x
git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
git cherry-pick -x -m1 c4a24d29bc47a673a3d84980c8d9a8a9040dc076
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
git commit -am 'Backport PR #49377: BUG: Fix passing `Colormap` instance to plot methods with mpl >= 3.6'
```

4. Push to a named branch:

```
git push YOURFORK 1.5.x:auto-backport-of-pr-49377-on-1.5.x
```

5. Create a PR against branch 1.5.x, I would have named this PR:

> "Backport PR #49377 on branch 1.5.x (BUG: Fix passing `Colormap` instance to plot methods with mpl >= 3.6)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the `Still Needs Manual Backport` label once the PR gets merged.

If these instructions are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 @zmoon would you have time to follow the instructions above to submit a backporting PR to target the 1.5.x branch? @mroeschke happy to have a go