[FIX] pos_mercury: Wrong use of popup method

Fixed the popup call. The call was made with the old method showPopup.

The call is now made with the new .add method on the popup service.

closes odoo/odoo#120274

X-original-commit: d174e6cdacfdde6973e4ced931bb7572b6bd0511
Signed-off-by: Samuel Degueldre <sad@odoo.com>
Signed-off-by: Monnom David (moda) <moda@odoo.com>

addons/pos_mercury/static/src/js/PaymentScreen.js

@@ -245,7 +245,7 @@ patch(PaymentScreen.prototype, "pos_mercury.PaymentScreen", {
         // the transaction deferred is used to update transaction status
         // if we have a previous deferred it indicates that this is a retry
         if (!old_deferred) {
-            self.showPopup(PaymentTransactionPopup, {
+            this.popup.add(PaymentTransactionPopup, {
                 transaction: def,
             });
             def.notify({