The 'destroy' signal currently doesn't work with connectObject(),
because the handler is only connected after the signal tracker's
own destroy handler, which disconnects all handlers.
Address this by using connect_after for the cleanup handler, so
that other destroy handlers run before it (unless they also use
ConnectFlags.AFTER, but well *shrug*).
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2221>
7b0a94b246