Updated potx lib header

assets/lib/potx/potx.php

 <?php
 // $Id: potx.inc,v 1.1.2.17.2.7.2.19.2.16 2011/01/26 12:16:06 goba Exp $
 
+/**
+ * This file contains a modified version of GPL code. The original code for Translation template extractor@7.x-1.0 (available here: https://git.drupalcode.org/project/potx/)
+ * has been modified in December 2022. Modifications copyright (C) 2023 European Union.
+ */
+
 /**
  * @file
  *   Extraction API used by the web and command line interface.