New face `mode-line-active` with variable pitch in emacs git/29.1

[Tim Ruffing]

With the current emacs 29.1 (unreleased), the font in the mode-line is not monospace anymore:

This is due to a recent addition of a face mode-line-active which inherits from variable-pitch. I could describe the issue in more detail but the friends at doom have a great bug report: doomemacs/themes#689

I reported this in spacemacs first (syl20bnr/spacemacs#15206) but here is the better place. Maybe this should be fixed in (all?) themes. But I can imagine that some workaround in spaceline could be helpful because this will affect a lot of themes until they've all been fixed.

In doom, they recommend this workaround for the user:
(set-face-attribute 'mode-line-active nil :inherit 'mode-line)