feat: sort criteria 'Headline' shoud map to 'sp_sortvalue'

src/Service/Search/Schema2xFieldMapper.php

@@ -104,7 +104,7 @@ public function getSortField(Criteria $criteria): string
             case $criteria instanceof Name:
                 return 'sp_name';
             case $criteria instanceof Headline:
-                return 'sp_title';
+                return 'sp_sortvalue';
             case $criteria instanceof Date:
                 return 'sp_date';
             case $criteria instanceof Natural: