[FIX] pos_restaurant: fix blank receipt print

Current behavior:
When trying to print the bill in PoS restaurant from a mobile device,
the bill appears completely blank.

Steps to reproduce:
- Open Odoo on mobile device
- Go to PoS restaurant
- Create an order
- Click on the "Bill" button
- Click on the "Print" button
- The bill is completely blank

This is happening because on mobile after clicking on the "Print" button
the pos directly return to the order screen. What happens when you do
`window.print()` is you basically do a screenshot of the screen with
some specific CSS rules. But on mobile, we go back too fast on the order
screen and the screenshot is empty.

opw-3507918

closes odoo/odoo#138282

X-original-commit: ebf214944097b9731a2a5dcf53d367715ceb8a35
Signed-off-by: Vlad Stroia (vlst) <vlst@odoo.com>
Signed-off-by: Robin Engels (roen) <roen@odoo.com>

addons/pos_restaurant/static/src/app/bill_screen/bill_screen.js

@@ -6,8 +6,10 @@ import { registry } from "@web/core/registry";
 export class BillScreen extends ReceiptScreen {
     static template = "pos_restaurant.BillScreen";
     confirm() {
-        this.props.resolve({ confirmed: true, payload: null });
-        this.pos.closeTempScreen();
+        if (!this.env.isMobile) {
+            this.props.resolve({ confirmed: true, payload: null });
+            this.pos.closeTempScreen();
+        }
     }
     /**
      * @override