[FIX] hr: onchange department don't reset manager

We should avoid reseting the manager_id on the employee when there is no
manager defined on the department

Also updates the department form view in order to display the fields
better

closes odoo/odoo#37028

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

addons/hr/models/hr_employee.py

@@ -220,7 +220,8 @@ class HrEmployeePrivate(models.Model):
 
     @api.onchange('department_id')
     def _onchange_department(self):
-        self.parent_id = self.department_id.manager_id
+        if self.department_id.manager_id:
+            self.parent_id = self.department_id.manager_id
 
     @api.onchange('user_id')
     def _onchange_user(self):

addons/hr/views/hr_department_views.xml

@@ -8,8 +8,8 @@
                 <form string="department">
                     <sheet>
                         <widget name="web_ribbon" text="Archived" bg_color="bg-danger" attrs="{'invisible': [('active', '=', True)]}"/>
+                        <field name="active" invisible="1"/>
                         <group col="4">
-                            <field name="active" invisible="1"/>
                             <field name="name"/>
                             <field name="manager_id"/>
                             <field name="parent_id"/>