[FIX] purchase: wrong get 'group_id'
[FIX] purchase: wrong get 'group_id'

The error before this pr could be reproduce with the steps,
- Create two warehouse WA and WB
- Create Route to get: Purchase in WA and transfer to WB
- Create product with Route created before
- Create orderpoint to WB
- Run scheduler

If there is no purchase created the `_run_buy` method tries to create a
PO, but if there is no `group_id`, a traceback occurs.

Closes #24353
opw-1838384

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo