[contract] reactivate the closed contract at the SO's confirmation

- Task: https://www.odoo.com/web?debug=#id=6527&view_type=form&model=project.task&action=327
- Pad: https://pad.odoo.com/p/r.hhgH3UWxNoWzXLBT
Use `_` to ignore a return value: `_, tree_view_id = ir_model_data_obj.get_object_reference(…)`