type_very_safely: use looser still screen similarity
    
    type_very_safely commonly gets stuck waiting on a still screen
    at the end because when you're typing, there's often a flashing
    cursor, and the default similarity for wait_still_screen is 47
    which is tight enough that a flashing cursor usually fails it.
    So back it off to 45.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>