BUG: fix boxplot column misorder

[zhuoyahuang]

• closes BUG: xticklables is not correctly set when using df.plot.box with group-by  #50427 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

the data.column is MultiIndex, for example

data.columns: MultiIndex([('c', 'value'),
        ('b', 'value'),
        ('a', 'value')],
       )

The problem with the original code is not respecting the order of by

expected output from the original issue

[WillAyd]

Can you add a changelog entry for 3.0.0? Also looks like this caused some regressions

[github-actions]

This pull request is stale because it has been open for thirty days with no activity. Please update and respond to this comment if you're still interested in working on this.

[zhuoyahuang]

still working on it, im gonna address Will's comment