[FIX] pos_loyalty: fix typo in pos_loyalty

Current behavior:
If you create an empty Db and just create one coupon program for the PoS
, the `enter_code` button is not displayed. This happens because the
condition to show the button was looking for program type `coupon`
instead of `coupons`.

Steps to reproduce:
- Create an empty Db (Important)
- Install PoS and PoS Loyalty
- Create a coupon program for the PoS
- Open the PoS, the `enter_code` button is not displayed

opw-3078726

closes odoo/odoo#106585

Signed-off-by: Trinh Jacky (trj) <trj@odoo.com>

addons/pos_loyalty/static/src/js/ControlButtons/PromoCodeButton.js

@@ -31,7 +31,7 @@ PromoCodeButton.template = 'PromoCodeButton';
 ProductScreen.addControlButton({
     component: PromoCodeButton,
     condition: function () {
-        return this.env.pos.programs.some(p => ['coupon', 'promotion', 'gift_card'].includes(p.program_type));
+        return this.env.pos.programs.some(p => ['coupons', 'promotion', 'gift_card'].includes(p.program_type));
     }
 });