Update conferences

Author: kjaymiller

_data/conferences.yml

@@ -1,7 +1,7 @@
 - dates: 22 - 25 Sep 2024
   location: Durham, North Caroline, United States
   name: DjangoCon US 2024
-  speaking: _No response_
+  speaking: Not Available
   summary: DjangoCon US 2024 has been announced! Join us for five days of inspiration,
     education, and networking opportunities centering around the Django web framework.
   type: both