[FIX] hr_contract: Track employee_id modification on contracts

closes odoo/odoo#34483

Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/hr_contract/models/hr_contract.py

@@ -63,7 +63,7 @@ class Contract(models.Model):
 
     name = fields.Char('Contract Reference', required=True)
     active = fields.Boolean(default=True)
-    employee_id = fields.Many2one('hr.employee', string='Employee')
+    employee_id = fields.Many2one('hr.employee', string='Employee', tracking=True)
     department_id = fields.Many2one('hr.department', string="Department")
     type_id = fields.Many2one('hr.contract.type', string="Employee Category", required=True, default=lambda self: self.env['hr.contract.type'].search([], limit=1))
     job_id = fields.Many2one('hr.job', string='Job Position')