MDL-81520 core: Fix test finality

question/format/xml/tests/xmlformat_test.php

@@ -46,7 +46,7 @@ require_once($CFG->dirroot . '/question/engine/tests/helpers.php');
  * @copyright  2009 The Open University
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class xmlformat_test extends \question_testcase {
+final class xmlformat_test extends \question_testcase {
     public function assert_same_xml($expectedxml, $xml) {
         $this->assertEquals(str_replace("\r\n", "\n", $expectedxml),
                 str_replace("\r\n", "\n", $xml));