Steps to reproduce the bug:
Let's consider a product P with a unit price = 10
- Create a SO for two lines of the same product P
- Validate the SO and create the invoice
- Refund the invoice and validate it
- Go to Reporting > Sale report and select "Invoiced amount" as measures
Bug= -20 was displayed for the invoiced amount.
Technically, the two refund invoice lines of P were used two times in function
_compute_invoice_amount because for each SO line we catched all the refund lines
of the same product.
opw:1906445
closesodoo/odoo#29095