[DL]String additions to 'gnome-control-center.master'

[GNOME Status Pages <noreply gnome org>]

This is an automatic notification from status generation scripts on:
https://l10n.gnome.org.

There have been following string additions to module 'gnome-control-center.master':

+ "The username should usually only consist of lower case letters from a-z, digits and the following 
characters: - _"

Note that this doesn't directly indicate a string freeze break, but it
might be worth investigating.
https://gitlab.gnome.org/GNOME/gnome-control-center/commits/master