update summit social activities

Signed-off-by: Birgit Brecknell <b@brck.nl>

Foundation/Summit/2024/social-activities.html

@@ -21,7 +21,7 @@ <h3>
     A number of informal social activities are being organised by local Sydney-siders. Check out the list and contact the organiser to register your interest.
 </p>
 <p>
-    This list is in chronological order. Note that some activities require advanced bookings, by 20 September 2024.
+    This list is in chronological order. Note that some activities require advanced bookings, by <s>20 September 2024</s> 4 October 2024.
 </p>
 <ul>
     <li><a href="#blue-mountains">Blue Mountains bush walk</a>, 13 Oct, Free</li>