[FIX] hr: tz on user required in view because of resource mixin

In the user preference, change the timezone of the user to blank (False value)
Save

Before this commit, a cryptic error was raised because the field tz in
resource.resource is required
Note that when writing on res.user, we write some fields (including tz)
on hr.employee, which is a resource.mixin, and therefore uses resource.resource

After this commit, we make the field required in the view

OPW 1934462

closes odoo/odoo#31312

addons/hr/views/hr_views.xml

@@ -624,6 +624,17 @@
             </field>
         </record>
 
+        <record id="view_users_form_simple_modif_resource" model="ir.ui.view">
+            <field name="name">res.users.preferences.form.resource</field>
+            <field name="model">res.users</field>
+            <field name="inherit_id" ref="base.view_users_form_simple_modif" />
+            <field name="arch" type="xml">
+                <field name="tz" position="attributes">
+                    <attribute name="required">1</attribute>
+                </field>
+            </field>
+        </record>
+
         <menuitem
             action="open_module_tree_department"
             id="menu_hr_department_tree"