[FIX] account: keep receivable account on duplicate invoice

Steps to reproduce:
* create an invoice with a line
* change the receivable account
* duplicate the invoice

Result: the receivable account is recomputed to the default one.
Expected: we should keep it.

task-3504443

closes odoo/odoo#135366

Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>