Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2416>
and the subsurface was not previously detached from it using `wl_subsurface_destroy()`. Without 'window-actor/wayland: Remove subsurface actors on dispose' this test would fail. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1958>