chore: update CHANGELOG

Author: jpraynaud

mithril-stm/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](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.5.4 (10-07-2025)
+
+### Added
+
+- Added golden tests for JSON (de)serialization.
+
 ## 0.5.3 (10-07-2025)
 
 ### Added