Description:
------------
https://3v4l.org/itLi1

I guess the change was introduced by https://github.com/php/php-src/pull/2499

Test script:
---------------
<?php

$it = new \AppendIterator();
$it->append(new ArrayIterator(['foo']));

foreach ($it as $item) {
    echo $item;
    
    if ('foo' === $item) {
        $it->append(new ArrayIterator(['bar']));
    }
}

Expected result:
----------------
foobar

Actual result:
--------------
foo