Update CHANGES.md

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

Author: jberdine

CHANGES.md

@@ -3,7 +3,7 @@
 ### Added
 
 - Support `.gitattributes` `export-ignore` attribute to exclude files from
-  distribution archives (#<PR_NUMBER>, @jberdine)
+  distribution archives (#515, @jberdine)
 - Add `dune-release delegate-info version` to show the current version as infered
   by the tool (#495, @samoht)
 - Add `--dev-repo` to `dune-release` and `dune-release publish` to overwrite