[FIX] purchase: change invoice date
[FIX] purchase: change invoice date

- Create a PO, generate the vendor bill
- Change a price unit
- Change the invoice date

The price unit is reset to the PO value.

We only recompute it if the currency of the invoice is different from
the currency of the PO.

Fixes #22164
opw-804894

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