pt-online-schema-change not working with MariaDB 10.x

   if ($server_version >= '8.0' && $alter_fk_method eq 'drop_swap') {
       my $msg = "--alter-foreign-keys-method=drop_swap doesn't work with MySQL 8.0+\n".
                 "See https://bugs.mysql.com/bug.php?id=89441";
       die($msg);
   }