[app_dart] Fix publish topic name for github webhooks (#2102)

diff --git a/app_dart/lib/src/request_handlers/github_webhook.dart b/app_dart/lib/src/request_handlers/github_webhook.dart
index a1e399d..762438b 100644
--- a/app_dart/lib/src/request_handlers/github_webhook.dart
+++ b/app_dart/lib/src/request_handlers/github_webhook.dart
@@ -42,7 +42,7 @@
       ..event = event
       ..payload = requestString;
     log.fine(message);
-    await pubsub.publish('github-wehbooks', message.writeToJsonMap());
+    await pubsub.publish('github-webhooks', message.writeToJsonMap());
 
     return Body.empty;
   }