Added missing array key to $JUNIT

Author: mbeccati

run-tests.php

@@ -2636,6 +2636,7 @@ function junit_init() {
 			'test_fail'     => 0,
 			'test_error'    => 0,
 			'test_skip'     => 0,
+			'test_warn'     => 0,
 			'execution_time'=> 0,
 			'suites'        => array(),
 			'files'         => array()