[FIX] account: allow invoice report modification
[FIX] account: allow invoice report modification

The invoice lines table in the invoice report was using a `t-attf-class` where
it is not needed. It could be simplified with `class` instead.

This small simplification allows the user to modify the table with the Report
designer in Studio.

closes odoo/odoo#27978
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo