Fix sending notification upon rebase
    
    This basically redoes the work from 1ed1ef897a090b5e4513cf7cf53526a39eb1d068
    which was undone (by accident) in 4517cde766c746c4897996d5b6ff6ae512c4ded3
    I guess because of a wrong rebase or so.
    
    Fixes https://pagure.io/pagure/issue/3684
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>