Update type of property DOMElement::$attributes in attribute

Author: isfedorov

dom/dom_c.php

@@ -1724,7 +1724,7 @@ class DOMElement extends DOMNode implements DOMParentNode, DOMChildNode
      * A <classname>DOMNamedNodeMap</classname> containing the attributes of this node (if it is a <classname>DOMElement</classname>) or NULL otherwise.
      * @link https://php.net/manual/en/class.domnode.php#domnode.props.attributes
      */
-    #[LanguageLevelTypeAware(['8.1' => 'DOMNamedNodeMap'], default: '')]
+    #[LanguageLevelTypeAware(['8.1' => 'DOMNamedNodeMap|null'], default: '')]
     public $attributes;
 
     /**