Fix quoting of TZID in the .ics according to the validator at

icalendar.org
 - Legacy-Id: 18435

Author: OleLaursen

ietf/templates/meeting/agenda.ics

@@ -8,8 +8,8 @@ SUMMARY:{% if item.session.name %}{{item.session.name|ics_esc}}{% else %}{% if n
 {% if item.timeslot.show_location %}LOCATION:{{item.timeslot.get_location}}
 {% endif %}STATUS:{{item.session.ical_status}}
 CLASS:PUBLIC
-DTSTART{% if schedule.meeting.time_zone %};TZID="{{schedule.meeting.time_zone}}"{%endif%}:{{ item.timeslot.time|date:"Ymd" }}T{{item.timeslot.time|date:"Hi"}}00
-DTEND{% if schedule.meeting.time_zone %};TZID="{{schedule.meeting.time_zone}}"{%endif%}:{{ item.timeslot.end_time|date:"Ymd" }}T{{item.timeslot.end_time|date:"Hi"}}00
+DTSTART{% if schedule.meeting.time_zone %};TZID={{schedule.meeting.time_zone|ics_esc}}{%endif%}:{{ item.timeslot.time|date:"Ymd" }}T{{item.timeslot.time|date:"Hi"}}00
+DTEND{% if schedule.meeting.time_zone %};TZID={{schedule.meeting.time_zone|ics_esc}}{%endif%}:{{ item.timeslot.end_time|date:"Ymd" }}T{{item.timeslot.end_time|date:"Hi"}}00
 DTSTAMP:{{ item.timeslot.modified|date:"Ymd" }}T{{ item.timeslot.modified|date:"His" }}Z{% if item.session.agenda %}
 URL:{{item.session.agenda.get_versionless_href}}{% endif %}
 DESCRIPTION:{{item.timeslot.name|ics_esc}}\n{% if item.session.agenda_note %}