[FIX] repair: prevent cancelling a completed repair order

Steps to reproduce the bug:
- Create a repair:
    - Add any product to repair
    - Add any other product as part of the repair
    - Confirm the repair
    - Start the repair
    - End repair

Problem:
The cancel button becomes visible and clicking on it won't cancel the
moves, so it doesn't make sense to cancel a finished repair.

opw-3146606

closes odoo/odoo#111902

X-original-commit: 8d37cf46
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: Djamel Touati (otd) <otd@odoo.com>