[FIX] base: explicitly define Human Resources module category

As this category is used by `hr` module, we need to ensure the records
exists in database.
Even if the xmlid is automatically created if not present, it may be
deleted during upgrade (migration) if noupdate flag is not set in
database.

odoo/addons/base/data/ir_module_category_data.xml

@@ -66,6 +66,12 @@
             <field name="sequence">9</field>
         </record>
 
+        <record model="ir.module.category" id="module_category_human_resources">
+            <field name="name">Employees</field>
+            <field name="description">Helps you manage your employees.</field>
+            <field name="sequence">9</field>
+        </record>
+
         <record model="ir.module.category" id="module_category_hr_holidays">
             <field name="name">Leaves</field>
             <field name="description">Helps you manage your leaves.</field>