Update CHANGES.md to show issue #36470 is fixed in 2.69.0 release.

Author: jiangzzhu

CHANGES.md

@@ -99,6 +99,7 @@
 * PulsarIO has now changed support status from incomplete to experimental. Both read and writes should now minimally
   function (un-partitioned topics, without schema support, timestamp ordered messages for read) (Java)
   ([#36141](https://github.com/apache/beam/issues/36141)).
+* Fixed Spanner Change Stream reading stuck issue due to watermark of partition moving backwards ([#36470](https://github.com/apache/beam/issues/36470)).
 
 ## Known Issues