server-tools/excel_import_export_demo/report_action/partner_list/report.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
    <report id='action_report_partner_excel'
            string='Partner List (.xlsx)'
            model='report.partner.list'
            name='partner_list.xlsx'
            file='partner_list'
            report_type='excel'
    />
</odoo>