[FIX] hr_contract: fix demo contract starting

With the new year transition, some demo data relative to the current
time are now inconsistent with each others:

- Some payslips starts 2 mount before now.
- the contract starts this year, first January.

This means that
- the contract starts 2023-01-01
- the payslips ends 2022-12-01

Leading to an error
"The following employees have a contract outside of the payslip period"

Note that it looks like there is a also a demo/admin inconsistency
in data but this is out of the scope of this fix.

X-original-commit: ae259f93b6ccaaec17a8d32df6282278e015c395
Part-of: odoo/odoo#108884

addons/hr_contract/data/hr_contract_demo.xml

@@ -79,7 +79,7 @@
 
     <record id="hr_contract_qdp" model="hr.contract">
         <field name="name">Demo Contract</field>
-        <field name="date_start" eval="time.strftime('%Y')+'-1-1'"/>
+        <field name="date_start" eval="(DateTime.today() + relativedelta(years=-1, month=9))"/>
         <field name="employee_id" ref="hr.employee_qdp"/>
         <field name="job_id" model="hr.job"
             eval="obj().env.ref('hr.employee_qdp').job_id.id"/>