fix: update DOMDocument return values to support PHP 8.3

Previously, the return value was \DOMDocument for the static calls, but
it has been changed to just bool in PHP 8.3. Also, starting from PHP 8.0,
static calls to those methods throw an error, so changing the types
should not break previous versions.

src/MicrodataDOMDocument.php

@@ -22,7 +22,7 @@ public function getItems(): \DOMNodeList
      * {@inheritdoc}
      * Also assigns $xpath with DOMXPath of the freshly loaded DOMDocument.
      */
-    public function loadHTML($source, $options = 0): \DOMDocument|bool
+    public function loadHTML($source, $options = 0): bool
     {
         $return = parent::loadHTML($source, $options);
 
@@ -35,7 +35,7 @@ public function loadHTML($source, $options = 0): \DOMDocument|bool
      * {@inheritdoc}
      * Also assigns $xpath with DOMXPath of the freshly loaded DOMDocument.
      */
-    public function loadHTMLFile($filename, $options = 0): \DOMDocument|bool
+    public function loadHTMLFile($filename, $options = 0): bool
     {
         $return = parent::loadHTMLFile($filename, $options);