FIX: Duplicate error for chat messages for upload-only messages (#31539)

This commit fixes an issue where if you tried to post
2 chat messages in quick succession which only contained
uploads (both `message` fields would be `""`), then we
would show the "You posted an identical message too recently."
error.

We should not do this for upload-only messages, they
are not identical messages.

plugins/chat/app/models/chat/message.rb

@@ -168,6 +168,10 @@ module Chat
       Emoji.gsub_emoji_to_unicode(message).truncate(400)
     end
 
+    def only_uploads?
+      self.message.blank? && self.uploads.present?
+    end
+
     def to_markdown
       upload_markdown =
         self