Replace header alert back to JuliaCon (#2113)

index.html

@@ -14,7 +14,7 @@
     <div class="alert alert-dark alert-dismissible mb-0" role="alert">
 
       <p class="text-center">
-	      <a href="https://form.jotform.com/241373057274355">The 2024 Julia User & Developer Survey is now open! Click here to participate. </a>
+	      <a href="http://juliacon.org">JuliaCon 2024</a> is around the corner. <a href="https://www.tickettailor.com/events/numfocus1/1114995">Tickets</a> are on sale now.
       </p>
 
       <button type="button" class="close" data-dismiss="alert" aria-label="Close">