Adjust button title on the 'Fork and Edit' action
    
    When viewing the main project while the user already forked it, change
    the label of the button from "Fork and Edit" to "Edit in your fork"
    
    Fixes https://pagure.io/pagure/issue/2558
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>