<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <data>
        <template id="assets_backend" name="Custom_header_maintenance" inherit_id="web.assets_backend">
            <xpath expr=".">
                <script type="text/javascript" src="/custom_maintenance/static/src/js/views/fields/relational_fields.js"/>
            </xpath>
        </template>
    </data>
</odoo>