Add change to RELEASENOTES

Author: rohitjoins

RELEASENOTES.md

@@ -93,6 +93,8 @@
         ([#710](https://github.com/androidx/media/pull/710)).
     *   MIDI: Fix issue where seeking forward skips the Program Change events
         ([#704](https://github.com/androidx/media/issues/704).
+    *   Migrate to FFmpeg 6.0
+        ([#707](https://github.com/androidx/media/pull/707)).
 *   Leanback extension:
 *   Cast Extension:
     *   Sanitize creation of a `Timeline` to not crash the app when loading