[FIX] website_event: allow controller to read event.registration

The controller /event/<model("event.event"):event>/registration/confirm
was broken since the portal user cannot read event.registration objects.

In 9.0 this was not an issue as we browsed and sudoed the
event.registration, but since in 10.0 this line disapeared so did the
sudo which this commit reintroduces.

addons/website_event/controllers/main.py

@@ -255,6 +255,6 @@ class WebsiteEventController(http.Controller):
                 Attendees._prepare_attendee_values(registration))
 
         return request.render("website_event.registration_complete", {
-            'attendees': Attendees,
+            'attendees': Attendees.sudo(),
             'event': event,
         })