[IMP] web: Kanban: correct cover image margins
[IMP] web: Kanban: correct cover image margins

The cover image top and bottom margins should be the same on a kanban record.

The bottom margin on `o_attachment_image` has thus been removed as it is already
defined on `o_kanban_record_body` class, which makes a double bottom margin.

Task 54019

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