Update CHANGELOG

Author: phinner

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/),
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## v4.0.0-k.2.1.0 - 2024-12-03
+
+### Chores
+
+- Updated kotlin to `2.1.0` and serialization to `1.7.3`.
+
 ## v4.0.0-k.2.0.20 - 2024-09-17
 
 ### Features