add note that issue was only with php4

git-svn-id: https://svn.php.net/repository/pear/packages/XML_Parser/trunk@266397 c90b9560-bf6c-de11-be94-00142212c4b1

Author: ashnazg

tests/bug-9328.phpt

@@ -2,6 +2,10 @@
 XML Parser:  test for Bug #9328 "assigned by reference error in XML_RSS parse"
 --FILE--
 <?php
+/*
+ * this issue only exists in PHP4
+ */
+
 require_once 'XML/RSS.php';
 
 $url = 'www.someverybogusurl.com';