desktop_update_graphical: try to workaround GGO #2442
    
    In current F40 and Rawhide, this test is frequently failing
    because gnome-software is behaving weirdly at startup - the
    third-party software dialog moves around even more than before,
    the app seems to get stuck in the "not responding" state
    briefly sometimes, and there's a very weird state it gets into
    sometimes where the window is shorter than usual and clicks
    don't seem to register in the right place. While I'm trying to
    bisect these bugs, these magic voodoo incantations (tested on
    the staging instance) seem to mostly work around the weird
    behaviour, and setting RETRY=2 should backstop it a bit further.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>