web/web_ir_actions_act_window_page/views/assets.xml

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
    <template id="assets_backend"
              name="web_ir_actions_act_window_page assets"
              inherit_id="web.assets_backend">
        <xpath expr="." position="inside">
            <script type="text/javascript"
                    src="/web_ir_actions_act_window_page/static/src/js/web_ir_actions_act_window_page.js"></script>
        </xpath>
    </template>
</odoo>