Resolve #3490037 "Min drupal 10.3"

Closes #3490037

modules/private_message_notify/src/Service/PrivateMessageNotifierInterface.php

 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\private_message_notify\Service;
 
 use Drupal\private_message\Entity\PrivateMessageInterface;