Fix setting up the git hooks when there is no DOCS_FOLDER set
    
    This happens on pagure instance where the documentation hosting is
    disabled but that shouldn't prevent the git hooks from working most of
    the time.
    
    So we are testing that we do not fail to set up the hooks.
    
    Fixes https://pagure.io/pagure/issue/2462
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>