ref(replay): Ensure we only clear for buffer mode (#8744)

This _shouldn't_ happen, but it makes sense to guard so we only clear
the event buffer cache on checkouts when in `buffer` mode. I guess the
behavior of rrweb is not 100% defined in that it _cannot_ generate a new
checkout in non-buffer mode 🤔 better safe than sorry.

Author: mydea

packages/replay/src/util/addEvent.ts

@@ -40,7 +40,7 @@ export async function addEvent(
   }
 
   try {
-    if (isCheckout) {
+    if (isCheckout && replay.recordingMode === 'buffer') {
       replay.eventBuffer.clear();
     }