Update CHANGES.md

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: WardBrian

CHANGES.md

@@ -14,7 +14,7 @@ profile. This started with version 0.26.0.
   `let+ x in ...` when `letop-punning=always`. With `letop-punning=never`, it
   becomes `let+ x = x in ...`. The default is `preserve`, which will
   only use punning when it exists in the source.
-  This also applies to `let%ext` bindings (#<PR_NUMBER>, @WardBrian).
+  This also applies to `let%ext` bindings (#2747, @WardBrian).
 
 ### Fixed