[FIX] hr_holidays: make test_current_leave_status deterministic

The test_current_leave_status checks the correct implementation of different
hr.leave computed fields. To do this, a leave is created, during the test. The
test fails however, when the employee is not supposed to work during the leave
period, which can happen when running the test on certain days. The test is
made deterministic again by adding the number_of_days field to the dict. As
this is a stored field, the created leave entry will be considered valid.

closes odoo/odoo#121533

Signed-off-by: Kevin Baptiste <kba@odoo.com>