events: Add missing track_caller attribute

Without this one, the `#[track_caller]` in `make_reply_to` and
`make_reply_to_raw` were pointless.

crates/ruma-events/src/room/message.rs

@@ -277,6 +277,7 @@ impl RoomMessageEventContent {
         )
     }
 
+    #[track_caller]
     fn make_reply_fallback(mut self, original_event: OriginalEventData<'_>) -> Self {
         let empty_formatted_body = || FormattedBody::html(String::new());