[FIX] hr_holidays: incorrect number_of_hours_display

- Go to Settings > Technical > Resource > Working Times
- Have a Resource Calendar RC with Average hour per day != 8.00
- Have an Employee E with Working Hours == RC
- Leaves > Configuration > Leave Types
- Have a Leave Type LT with Take Leaves in Hours
- Leaves > Managers > All > Allocations
- Create an Allocation A with Employee E and Leave Type LT
- Enter any number in Duration

The number of hours entered changes as we leave the field.

Being totally honest, what happens here is not clear at all, but using
the corresponding `resource_id.calendar_id` field seems to fix the
problem.

opw-2191795

closes odoo/odoo#44903

X-original-commit: e239b354
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>