Tests: fix test_prefs for the new Gtk4 changes
- Check setup.ui with Gtk4 and Gdk4 instead of Gtk3.
- To load libadwaita (Adw) before running setup.ui validation.
- Fix rawhide GitLab CI setup: rawhide just renamed from "41" to "42" and the previous .gitlab-ci.yml config failed. Renamed "41" to "rawhide" and things seem to work.