Fix typo and button label on the bugzilla assignee feature
    
    Fix a typo in the title of the button used to edit/change the
    bugzilla assignee overrides.
    Change as well the label of the button from Update to Edit as
    the former seemed to imply to some people that it would go and
    fetch that information from somewhere else while it is meant
    to offer a way to edit the information.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>