Revert "Bump Go version to 1.23.6 (#30242)" (#30359)

This reverts commit acbbd4c58d.

server/channels/app/notification_push.go

@@ -859,7 +859,7 @@ func (a *App) buildFullPushNotificationMessage(c request.CTX, contentsConfig str
 		}
 	}
 
-	hasFiles := len(post.FileIds) > 0
+	hasFiles := post.FileIds != nil && len(post.FileIds) > 0
 
 	msg.Message = a.getPushNotificationMessage(
 		contentsConfig,