odoo/addons/base_calendar/static/src/xml/base_calender.xml

<?xml version="1.0" encoding="UTF-8"?>
<template>
    <t t-name="Many2Many_invite" >
        <t t-set="i" t-value="0"/>
        <t t-foreach="elements" t-as="el">
            <span class="oe_tag" t-att-data-index="i">
                <a t-attf-class="oe_invitation #{el[2]}"/>
                <t t-esc="el[1]"/>
            </span>
        <t t-set="i" t-value="i + 1"/>
        </t>
    </t>
    <t t-name="invitation_view">
        Testttt
     </t>
</template>