I am creating a custom module in Odoo for a faculty and y need to create 3 roles (groups): students, professors and admins. An user cannot have 2 roles at the same time, so it could only be either a teacher, a professor or an admin. I have defined the permisions in the following code. But for selecting those permissions, Odoo creates a view with checkboxes, where you can chose 2 or more roles at the same time, instead of a selection field (dropdown), I dont want that. How can I force Odoo to create a dropdown for the selection of those roles, so I can only select one

<record model="ir.module.category" id="module_category_faculty">
    <field name="name">Faculty</field>
    <field name="description">Faculty Roles</field>
    <field name="sequence">45</field>
</record>

<record id="group_faculty_student" model="res.groups">
    <field name="name">Student</field>
    <field name="category_id" ref="module_category_faculty"/>
</record>

<record id="group_faculty_professor" model="res.groups">
    <field name="name">Professor</field>
    <field name="category_id" ref="module_category_faculty"/>
</record>

<record id="group_faculty_admin" model="res.groups">
    <field name="name">Admin</field>
    <field name="category_id" ref="module_category_faculty"/>
</record>