UI freeze break request for g-c-c

["Tobias Bernard" <tobias bernard im>]

Hello release team,

The recent lock screen changes require some adjustments to the background settings panel, because the lock 
screen now uses a blurred version of the session wallpaper rather than a separate one. This means that we 
need to remove the lock screen wallpaper setting from control-center:

https://gitlab.gnome.org/GNOME/gnome-control-center/merge_requests/705

In order to make the overall layout work better with only one preview, we also need to change the thumbnails 
to a smaller size:

https://gitlab.gnome.org/GNOME/gnome-control-center/merge_requests/706

I'd like to ask for a freeze break for these relatively small changes, which are needed to avoid some pretty 
visible regressions in UX quality for the background panel. These are pure UI changes, and don't change or 
introduce new strings.

Both MRs are already reviewed by maintainers and ready to be merged.

Cheers,
Tobias