[PNG] Make sure you're using the right calendar.

Hello everyone,

Our meeting is tomorrow at 11am ET.
Make sure you use the W3C calendar for the meeting link
<https://www.w3.org/groups/wg/png/calendar/>.
(A while back, there was a separate calendar. It had a meeting link which
is no longer used. Feel free to delete your meeting calendar entry and
re-add it from the W3C calendar just to be sure.)