LibWeb: Fix DOMImplementation changing content type of wrong document

DOMImplementation.createDocument() should set the content type of the
newly created document, not replace the content type of the
DOMImplementation's own host document.

Userland/Libraries/LibWeb/DOM/DOMImplementation.cpp

@@ -40,11 +40,11 @@ NonnullRefPtr<Document> DOMImplementation::create_document(const String& namespa
     xml_document->set_origin(m_document.origin());
 
     if (namespace_ == Namespace::HTML)
-        m_document.set_content_type("application/xhtml+xml");
+        xml_document->set_content_type("application/xhtml+xml");
     else if (namespace_ == Namespace::SVG)
-        m_document.set_content_type("image/svg+xml");
+        xml_document->set_content_type("image/svg+xml");
     else
-        m_document.set_content_type("application/xml");
+        xml_document->set_content_type("application/xml");
 
     return xml_document;
 }