Fix XMLReader::expand() signature
Fix XMLReader::expand() signature

According to [documentation](https://secure.php.net/xmlreader.expand), `XMLReader::expand()` method takes an optional `DOMNode` argument.

Test case : https://phpstan.org/r/4acbc01009a8562bb9a963daa6675985
phpstan/phpstan,phpstan/phpstan,phpstan/phpstan,phpstan/phpstan