cockpit: wait longer for services screen to load
    
    It seems like it can be *really* slow on aarch64, since 218:
    https://github.com/cockpit-project/cockpit/issues/14840
    this should give it a total of 180 seconds on aarch64 (90 second
    still screen timeout plus 30 second assert_screen timeout, with
    1.5x scale).
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>