fix audit

Author: stephanediondev

src/Controller/ElasticsearchClusterController.php

@@ -592,7 +592,7 @@ public function audit(Request $request, string $elasticsearchUsername, string $e
 
                         if ('basic' != $license['type'] && true === isset($license['expiry_date_in_millis'])) {
                             $now = (new \Datetime());
-                            $expire = new \Datetime(date('Y-m-d H:i:s', intval(substr($license['expiry_date_in_millis'], 0, -3))));
+                            $expire = new \Datetime(date('Y-m-d H:i:s', intval(substr(strval($license['expiry_date_in_millis']), 0, -3))));
                             $interval = $now->diff($expire);
 
                             if (30 > $interval->format('%a')) {