[FIX] mrp: Allow multiple users to start the Work order

# Issue:
With User1, create a MO with work orders, and start one Work Order.
With User2, go to the MO, and start the same Work Order
=> Nothing happen, we currently prevent the workorders to have more than 1 open Time Tracking.

OPW-2845080

closes odoo/odoo#91033

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