[php-src] Issue #15331: dom: Element::$substitutedNodeValue test failed

Issue: https://github.com/php/php-src/issues/15331 Author: jtojnar ### Description Trying to package PHP 8.4 for testing on NixOS, when building the dom extension, I get the following failed test: ```php Element::$substitutedNodeValue [tests/modern/extensions/Element_substitutedNodeValue.phpt] ``` Looks like the tests is newly added in https://github.com/php/php-src/pull/14754 ### ext/dom/tests/modern/extensions/Element_substitutedNodeValue.out ```php string(1) "1" NULL <?xml version="1.0" encoding="UTF-8"?> <root>1</root> string(2) "<>" NULL <?xml version="1.0" encoding="UTF-8"?> <root>&lt;&gt;</root> string(0) "" NULL <?xml version="1.0" encoding="UTF-8"?> <root/> ``` ### ext/dom/tests/modern/extensions/Element_substitutedNodeValue.diff ```diff -- string(0) "" NULL <?xml version="1.0" encoding="UTF-8"?> 012- <root></root> 012+ <root/> ``` ### libxml2 version 2.13.3 ### PHP Version 8.4.0alpha4 ### Operating System NixOS