[FIX] account_check_printing: allow multiple payments

Apply next sequence check number with multiple payments

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 ...

Remove the action_post method as it was not necessary anymore
because we compute the check_number in the compute_check_number method.
The check number should be computed only if the payment is posted,
that's why we filter on payment state.

opw-2830586

closes odoo/odoo#90193

Signed-off-by: William André (wan) <wan@odoo.com>