[IMP] stock_landed_costs: set AML's account on its creation

[1] could be improved as we could even remove the `create` override
introduced by [2]. That way, we avoid:
- a useless `create` layer
- a possible write on an AML just after its creation

The method `_get_computed_account` is called during the AML creation
process:
https://github.com/odoo/odoo/blob/8c8d657c85f76bd74d663843382af3dde8d885b8/addons/account/models/account_move.py#L2058
https://github.com/odoo/odoo/blob/8c8d657c85f76bd74d663843382af3dde8d885b8/addons/account/models/account_move.py#L1933



Note: the test checks the use cases of both commits

[1] 66ea264f
[2] f36c5c8a

OPW-3251714

closes odoo/odoo#117920

Signed-off-by: William Henrotin (whe) <whe@odoo.com>