[FIX] mass_mailing_sale: use singleton instead of self when getting the UTM domain
[FIX] mass_mailing_sale: use singleton instead of self when getting the UTM domain

Purpose
=======
When computing some fields of the mailing, an error can occur if we
compute the fields in batch.

Task-2227411

closes odoo/odoo#52904

X-original-commit: 933a2f986a72ddb8610d7d93a078d2cb0cb10f16
Signed-off-by: Thibault Delavallee (tde) <2d325771bb6e8870d87f0f3f7b45589a8338e550@openerp.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo