When printing a draft invoice, it raises an error.

The error comes from fix #65320: the latter registers the printed
invoice as main attachment, but this needs to be done only with posted
invoices.

OPW-2427247

closes odoo/odoo#66526

X-original-commit: 192e128e
Signed-off-by: Laurent Smet <smetl@users.noreply.github.com>
Signed-off-by: Adrien Widart <adwid@users.noreply.github.com>