Add CHANGES.md note for BigQueryEnrichmentHandler duplicate-key batch fix (#38068)

* Add CHANGES.md note for BigQueryEnrichmentHandler duplicate-key fix

* Update CHANGES.md

---------

Co-authored-by: tvalentyn <tvalentyn@users.noreply.github.com>

Author: prabhnoor0212

CHANGES.md

@@ -80,7 +80,7 @@
 
 ## Bugfixes
 
-* Fixed X (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
+* Fixed BigQueryEnrichmentHandler batch mode dropping earlier requests when multiple requests share the same enrichment key (Python) ([#38035](https://github.com/apache/beam/issues/38035)).
 
 ## Security Fixes