[FIX] mrp: create WO when importing MO with BoM

To reproduce the issue:
(Need mrp_workorder. Use demo data)
1. Select an existing MO that has some WO
2. Action > Export:
    - Import-compatible export
    - Add "Bill of Material"
3. Import the exported file (remove the external id)
4. Open the new MO

Error: The WO are not created

OPW-2964632

closes odoo/odoo#99803

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