DOC: fix EX02 errors in docstrings
Related to the issue #51236

This PR enables functions:
`pandas.io.formats.style.Styler.concat`
`pandas.io.formats.style.Styler.export`
`pandas.io.formats.style.Styler.set_td_classes`
`pandas.io.formats.style.Styler.use`
> Actually, let's just take this - we'll fix EX03 errors when we fix EX03 errors
> 

I just created the change for the indentation issue.

And while running `python scripts/validate_docstrings.py pandas.io.formats.style.Styler.concat`
the missing whitespace error appeared in 3 other examples for `concat`, I corrected it as well.

Should I create a new PR for this? sure, thanks! or just include them in the next PR