update CHANGELOG

Author: damiannolan

CHANGELOG.md

@@ -48,6 +48,12 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Bug Fixes
 
+## [v6.3.1] - 2024-04-24
+
+### Improvements
+
+* (testing) [\#6179](https://github.com/cosmos/ibc-go/pull/6179) Add `Version` to tendermint headers in ibctesting.
+
 ## [v6.3.0](https://github.com/cosmos/ibc-go/releases/tag/v6.3.0) - 2024-04-05
 
 ## [v6.2.1](https://github.com/cosmos/ibc-go/releases/tag/v6.2.1) - 2023-10-20