[FIX] stock: set partner for inter-warehouse transfers

The inter-warehouse transfers do not have any partner defined.

To reproduce the issue:
(Let WH01 be the default warehouse)
1. In Settings, enable:
    - Multi-Warehouses
    - Multi-Step Routes
2. Create a second warehouse WH02
3. On WH2, enable "Resupply From WH01"
4. Create a product P:
    - Storable
    - Routes:
        - WH02: Supply Product from WH01
    - Reordering rules:
        - Min = Max = 1
        - Warehouse: WH02
        - Location: WH02/Stock
5. Update the quantity of P:
    - 1 x P in WH01/Stock
6. Run the scheduler
7. Open the generated pickings for P

Error: None of the picking has a `partner_id` ("Receive From"/"Delivery
Address")

Partial backport of af13e766

OPW-2779150

closes odoo/odoo#86998

X-original-commit: d67ec8d1
Signed-off-by: Steve Van Essche <svs@odoo.com>
Signed-off-by: Adrien Widart <awt@odoo.com>
Co-authored-by: yhu-odoo <yhu@odoo.com>