[FIX] pos_sale: fix test and traceback when pos_loyalty is not installed

Current behavior:
When pos_loyalty is not installed,the
`test_settle_order_with_promotions` was failing. Also if the user tries
to settle an order he would get a traceback.

The issue was introduced here: https://github.com/odoo/odoo/pull/119673



opw-3247545

closes odoo/odoo#121603

Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>