[FIX] stock_landed_costs: reconciliation with vendor bill

in anglo saxon accounting
- receipt products through an rfq
- when creating the vendor bill of the rfq, directly add a landed costs
  product
- post the vendor bill then create the landed cost, validate the landed
  cost
- the aml of the LC is not reconciled with the aml of the vendor bill
  for the lc product because the "You are trying to reconcile some
  entries that are already reconciled." error.

We fix this by filtering out the already reconciled aml.
Not that the flow is behaving as expected if the landed cost is created
in another vendor bill, such as the tests were doing. We thus add
another test.

opw-2184988