path: root/indoteknik_custom/views/assets.xml

<odoo>
    <template id="indoteknik_assets_backend" inherit_id="web.assets_backend" name="Indoteknik Custom Backend Assets">
        <xpath expr="." position="inside">
            <script type="text/javascript" src="/indoteknik_custom/static/src/js/check_product_barcode.js"/>
        </xpath>
    </template>
</odoo>