[skip ci] Add missing skipif for windows

Author: iluuu1994

ext/opcache/tests/gh21052.phpt

@@ -9,6 +9,10 @@ opcache.enable=1
 opcache.enable_cli=1
 opcache.file_cache="{TMP}"
 opcache.preload={PWD}/gh21052_a.inc
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY == 'Windows') die('skip Preloading is not supported on Windows');
+?>
 --FILE--
 <?php
 require __DIR__ . '/gh21052_b.inc';