Update structure.sql to match trigger function in migration

See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/51852#note_498957031

db/structure.sql

@@ -22,8 +22,8 @@ UPDATE projects SET has_external_issue_tracker = (
     WHERE project_id = COALESCE(NEW.project_id, OLD.project_id)
       AND active = TRUE
       AND category = 'issue_tracker'
-    )
   )
+)
 WHERE projects.id = COALESCE(NEW.project_id, OLD.project_id);
 RETURN NULL;