[FIX] sale_timesheet_margin: sale order line cost

Set Default UoM on Timesheet Settings page: Hours
Set [Employee] Timesheet Cost (HR Settings tab): 65.00/hour
Create a product [TEST] as follows:
- Product type: service
- Invoicing Policy: Based on Timesheets
- Create on Order: Project & Task
- Unit of Measure: Days
- Purchase UoM: Days
- Sales Price: 1.00
- Cost: 0.00
Create a sales order
Add an order line with product [TEST], quantity 1
Confirm. Project and task will be created
On the task add a 1 hour timesheet entry for [Employee]
Save and go back to the SO

Issue: SO line cost is incorrectly computed.

opw-3378688

closes odoo/odoo#134380

X-original-commit: cb551051
Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>