[FIX] mail: add missing call icon in the discuss sidebar

Following the discuss refactoring* the call icon in the discuss sidebar
has not been reimplemented.

This commit fixes this issue.

\* https://github.com/odoo/odoo/pull/110188

closes odoo/odoo#117464

Signed-off-by: Debondt Didier (did) <did@odoo.com>

addons/mail/static/src/web/discuss/sidebar.xml

@@ -104,6 +104,7 @@
                 t-on-click.stop="() => this.leaveChannel(thread)" title="Leave this channel" role="img"/>
             <div t-if="threadService.canUnpin(thread)" t-attf-class="fa fa-times ms-1" t-on-click.stop="() => threadService.unpin(thread)" title="Unpin Conversation" role="img"/>
         </div>
+        <div t-if="Object.keys(thread.rtcSessions).length > 0" class="fa fa-volume-up ms-1 me-3" t-att-class="{ 'text-danger': rtc.state.channel?.id === thread.id }"/>
         <div t-if="counter > 0" t-attf-class="o-mail-DiscussCategoryItem-counter badge rounded-pill text-bg-primary ms-1 me-3">
             <t t-esc="counter"/>
         </div>