Add missing cache invalidation for innerHTML (#16652)

* Add test with wrong output

* Add missing cache invalidation for innerHTML

ext/dom/inner_html_mixin.c

@@ -359,6 +359,9 @@ zend_result dom_element_inner_html_write(dom_object *obj, zval *newval)
 		}
 	}
 
+	ZEND_ASSERT(obj->document != NULL);
+	php_libxml_invalidate_node_list_cache(obj->document);
+
 	dom_remove_all_children(context_node);
 	return php_dom_pre_insert(obj->document, fragment, context_node, NULL) ? SUCCESS : FAILURE;
 }

ext/dom/tests/modern/common/innerHTML_cache_invalidation.phpt

@@ -0,0 +1,27 @@
+--TEST--
+$innerHTML cache invalidation
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+$dom = Dom\XMLDocument::createFromString('<root><a/><a/><a/></root>');
+$els = $dom->getElementsByTagName('a');
+var_dump($els[0]->tagName);
+
+$dom->documentElement->innerHTML = '<b/>';
+
+echo $dom->saveXML(), "\n";
+var_dump($els);
+var_dump($els[0]?->tagName);
+
+?>
+--EXPECT--
+string(1) "a"
+<?xml version="1.0" encoding="UTF-8"?>
+<root><b/></root>
+object(Dom\HTMLCollection)#2 (1) {
+  ["length"]=>
+  int(0)
+}
+NULL