[FIX] website_event: correct inverse method
[FIX] website_event: correct inverse method

To work on multiple records at the same time.
Worked on a recordset but left some `self` calls.

Closes #25788

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo