This isn't really needed but will help reduce the size of
the container volume we will leave behind in the gitlab-runner,
without having to run a system-wide prune.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-session/-/merge_requests/110>

Allow to disable X11 sessions
CI updates
Translation updates

Also always install gnome-session-inhibit and optionally
gnome-session-selector.

Add back gnome-session-ctl (oops)