[FIX] purchase_stock: fix unexpected access right issue

Prerequisites -->

1) Login with a user with just Inventory/User access rights
2) Product A with purchase policy set to `on ordered quantities`
3) Product category of A set to `AVCO` costing method

Steps -->

1) Create+confirm a PO with product A and create and confirm vendor bill
2) Switch to Inventory/User user
3) Try to validate picking
4) Access right error

This occurs due to the fact that `Inventory/User` does not have access to s`tock.valuation.layer` or `account.move.line`.

Solution -->

Add sudo to the lines where accesses to SVL and invoice lines are made.

opw-3357028

closes odoo/odoo#129184

Signed-off-by: Arnold Moyaux (arm) <arm@odoo.com>