[skip ci] Add xleak to xml test due to libxml2 bug

Author: iluuu1994

ext/dom/tests/modern/xml/XMLDocument_fromString_04.phpt

@@ -2,6 +2,10 @@
 DOM\XMLDocument::createFromString 04
 --EXTENSIONS--
 dom
+--SKIPIF--
+<?php
+if (getenv('SKIP_ASAN') && LIBXML_VERSION < 20911) die('xleak leaks under libxml2 versions older than 2.9.11');
+?>
 --FILE--
 <?php