[FIX] stock_landed_costs: cost account when dropship

- Set FIFO as costing method in product category
- Create a stockable product with the category configured previously
- Create a SO with the stockable product for 1 unit with dropship route
  and confirm the SO
- Confirm the PO created from the Sale Order to generate the delivery
- Process the stock picking
- Create a new Landed Cost with the stock picking delivered with a cost
  line with split method "Equal".
- Generate the valuation adjustments and confirm the landed cost to
  generate the journal entry

The debit account is wrong because the system takes the inventory
valuation account instead the expense account.

Odoo must take the expense account because the product never enter to
the company inventory, so is a cost of sale.

opw-1922633

closes odoo/odoo#29947