[FIX] account_check_printing: allow multiple payments

With this commit, we allow mutliple payments with manual
check printing.

Steps to reproduce:

- With manual check numbering
- Create +=3 vendor bills
- In bills list view, select all bills and register payment
- Select Checks as payment methos, and validate
-> Validation Error: The following numbers are already used ...

Setting the check_numbers before calling the super of
payment.action_post.

opw-2830586

closes odoo/odoo#91128

X-original-commit: c26cd9fa
Signed-off-by: Florian Gilbert <flg@odoo.com>
Signed-off-by: Guillaume Vanleynseele <guva@odoo.com>