Meta: Fix “shadow-including-ancestors-descendant” generator check

This change fixes the IDLGenerators.cpp implementation of the “If
reflectedTarget's explicitly set attr-element is a descendant of any of
element's shadow-including ancestors” step from the “If a reflected IDL
attribute has the type T?, where T is either Element or an interface
that inherits from Element” case in the HTML spec at
http://whatwg.org/html/#reflecting-content-attributes-in-idl-attributes

Meta/Lagom/Tools/CodeGenerators/LibWeb/BindingsGenerator/IDLGenerators.cpp

@@ -3821,7 +3821,7 @@ JS_DEFINE_NATIVE_FUNCTION(@class_name@::@attribute.getter_callback@)
                 attribute_generator.append(R"~~~(
     auto const explicitly_set_attr = TRY(throw_dom_exception_if_needed(vm, [&] { return impl->@attribute.cpp_name@(); }));
     if (explicitly_set_attr) {
-        if (&impl->shadow_including_root() == &explicitly_set_attr->shadow_including_root()) {
+        if (&impl->shadow_including_root() == &explicitly_set_attr->root()) {
             retval = explicitly_set_attr;
         } else {
             retval = GC::Ptr<Element> {};