gs-age-rating-context-dialog: Fix coalescing groups when rating is lower

When the age rating of one group is lower than the group it’s to be
coalesced into, it should still be coalesced. Previously, coalescing
would only happen if the ages were identical.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Fixes: #1565
3 jobs for backport-1135-coalesce-groups-gnome-41 in 8 minutes and 18 seconds (queued for 7 seconds)
Status Name Job ID Coverage
  Build
passed debian-stable-x86_64 #1663592

00:02:56

passed fedora-x86_64 #1663591

00:08:18

manual flatpak bundle #1663593
flatpak allowed to fail manual