chore: Add missing license header

test/unit/models/classes/xml/XmlEditorTest.php

@@ -1,5 +1,23 @@
 <?php
 
+/**
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; under version 2
+ * of the License (non-upgradable).
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * Copyright (c) 2020-2023 (original work) Open Assessment Technologies SA.
+ */
+
 namespace oat\taoQtiTest\test\unit\models\classes\xml;
 
 use core_kernel_classes_Resource;