[FIX] l10n_latam_invoice_document: refund doc type

Prior to this change, if the user use a full refund option and choose a document type different than default one, the default document type was use regardless of the choosen one.

This was broken on this commit dfd01b8c#diff-1369ca152be95632086495cfcfbd54a0d18d893c2389670ff1d516f1596f3e0d

As l10n_latam_document_type_id is not stored, it's change is not saved and sended to to backend. We make this hack so that we don't break stable policy

This should be FP only till v15, on master this should be applied https://github.com/odoo/odoo/pull/82670



closes odoo/odoo#82931

Signed-off-by: Josse Colpaert <jco@odoo.com>