[FIX] sale,sale_project : Avoid sending multiple email on upsell

Expected behaviour:
When you create a sale order with a project associated. When the sale order change state
from non upsell to upsell sales person should receive one email.

Current behaviour:
The sales person receive an email for every entry in the timesheet after the sale order goes
from non upsell to upsell.

Step to reproduce:
Create a sale order setup to create a project and task and the invoicing policy is ordered quantities.

Add a timesheet entry which takes it past the ordered quantity.

Create the invoice for the order.

The state of the line and order goes to upsell, and the upsell email is sent to the salesperson.

Add another line in the timesheet and the email is sent again to the salesperson

closes odoo/odoo#78457

Signed-off-by: Laurent Stukkens (ltu) <ltu@odoo.com>