There's a few cbook.warn_deprecated calls that still use more than one positional argument, but the definition does not allow more than one positional argument:

def warn_deprecated(
        since, *, message='', name='', alternative='', pending=False,
        obj_type='attribute', addendum='', removal=''):

See https://lgtm.com/projects/g/matplotlib/matplotlib/alerts/?mode=list&rule=py%2Fcall%2Fwrong-arguments for a full list (10 as of writing, all instances of the alert were from this function). Some examples as of 6a61f93 include

• https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/offsetbox.py#L1245-L1248
• https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/axes/_base.py#L1313-L1314
• https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/axis.py#L1639-L1642

I think most (all?) of these were introduced during #12440, probably just some missed find/replacements.