Fix the unit-tests for the drop of the requests_session argument
    
    In 993137aa18fa19917b37dff5dfd7e93925728c5a we removed the
    requests_session from the list of arguments passed onto
    _is_retired_in_dist_git (which didn't accept that argument) but we had
    not adjusted the tests.
    This commit addresses that.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>