Fix warning jinga2.escape DeprecationWarning
    
    For example
    
    ./pagure/ui/filters.py:580: DeprecationWarning: 'jinja2.escape' is
    deprecated and will be removed in Jinja 3.1. Import 'markupsafe.escape'
    instead.
        output = escape(author.name)
    
    Signed-off-by: Dominik Wombacher <dominik@wombacher.cc>