[FIX] website_event_sale: event discount
[FIX] website_event_sale: event discount

Fine-tuning 180866fe1e3b8998cc47ee584abaaff76d4135bb

- Go to Sales > Configuration > Settings
- Enable "Multiple Sales Prices per Product" and select option "Prices
computed from formulas (discounts, margins, roundings)"
- Go to Sales > Catalog / Pricelists
- Select "Public Pricelist" and set "Discount Policy: Show public price
& discount to the customer"
- Add a discount to an event (20 % to "Open Days in Los Angeles" for
example)
- Go to the eCommerce, buy a ticket to "Open Days in Los Angeles" which
as a 20 % discount

Since 180866fe1e3b8998cc47ee584abaaff76d4135bb the discount is applied
two times.

opw-2058709

closes odoo/odoo#36106

Signed-off-by: Nicolas Martinelli (nim) <771435c469f83f6aa9c405ac5e1ed06314a94f2d@odoo.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo