[FIX] website_event: do not copy menu_id

When the user duplicates an event, the `menu_id` is copied. This causes
two issues. First, it links the event to the wrong menu. Then, the
controller `event` uses this `menu_id` to compute the target URL. It
will therefore redirect the user to the wrong event page.

opw-670353

addons/website_event/models/event.py

@@ -36,7 +36,7 @@ class event(models.Model):
     show_menu = fields.Boolean('Dedicated Menu', compute='_get_show_menu', inverse='_set_show_menu',
                                help="Creates menus Introduction, Location and Register on the page "
                                     " of the event on the website.", store=True)
-    menu_id = fields.Many2one('website.menu', 'Event Menu')
+    menu_id = fields.Many2one('website.menu', 'Event Menu', copy=False)
 
     @api.one
     def _get_new_menu_pages(self):