[FIX] pos_self_order: fix self order on iOS

Current behavior:
When adding a product with a variant, the variant page is not displayed
correctly, it's missing the add to cart button.

Steps to reproduce:
- Create a product with a multi checkbox variant
- Open self order menu on iOS
- Click on the product
- The "Add to cart" button is missing from the page

opw-3614337

closes odoo/odoo#148861

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

addons/pos_self_order/static/src/app/pages/product_page/product_page.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <templates id="template" xml:space="preserve">
     <t t-name="pos_self_order.ProductPage">
-        <div class="d-flex flex-column bg-view flex-grow-1 vh-100">
+        <div class="d-flex flex-column bg-view flex-grow-1 h-100">
             <div class="d-flex align-items-center flex-shrink-0 justify-content-between gap-3 px-3 py-2 w-100 bg-view border-bottom overflow-x-auto z-index-1">
                 <button class="btn btn-secondary btn-lg px-3 text-nowrap" t-on-click="back">
                     <i class="oi oi-chevron-left" aria-hidden="true"/><span class="ms-2 d-none d-md-inline">Discard</span>