This change was made previously [0] but reverted as it caused the
title-bar to disappear on Ubuntu (see #121241).
Check if the value is set to GNOME delimited by `:`.
Previously checking the interfaces was used which has the down-side
that any compositor that adds `gtk_shell*` support may hang on startup
because of bugs in Blender/LIBDECOR as happened with WAYFIRE,
see reply to #76428.
[0]: 3a5389d5ab
2d152db090