[FIX] website_sale_stock: prevent buying consumable

- In Website > Settings, set 'Show inventory on website and prevent
  sales if not enough stock'
- Create a consumable product P, publish on the eCommerce
- As user 1, buy 1 units of P => validate the SO => 1 unit is reserved
- As user 2, add 1 unit of P to the cart. In the cart click on the `+`
  to add a unit

The product is removed from the cart.

This happens because `virtual_available` quantity is taken into account,
while it shouldn't be since it is a consumable.

opw-2245075

closes odoo/odoo#50428

X-original-commit: ec6f281f
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>