[FIX] event_sale: update registrations as sudo.

Consequence of 19878d0

addons/event_sale/models/sale_order.py

@@ -41,7 +41,7 @@ def _update_registrations(self, confirm=True, cancel_to_draft=False, registratio
         order line has a product_uom_qty attribute that will be the number of
         registrations linked to this line. This method update existing registrations
         and create new one for missing one. """
-        Registration = self.env['event.registration']
+        Registration = self.env['event.registration'].sudo()
         registrations = Registration.search([('sale_order_line_id', 'in', self.ids), ('state', '!=', 'cancel')])
         for so_line in self.filtered('event_id'):
             existing_registrations = registrations.filtered(lambda self: self.sale_order_line_id.id == so_line.id)