[TASK] Add missing header comment

Classes/EventListeners/RegisterIcons.php

@@ -2,6 +2,19 @@
 
 declare(strict_types=1);
 
+/*
+ * This file is part of the TYPO3 CMS project.
+ *
+ * It is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License, either version 2
+ * of the License, or any later version.
+ *
+ * For the full copyright and license information, please read the
+ * LICENSE.txt file that was distributed with this source code.
+ *
+ * The TYPO3 project - inspiring people to share!
+ */
+
 namespace MASK\Mask\EventListeners;
 
 use MASK\Mask\Enumeration\FieldType;