Update CHANGELOG.md

Author: mboudet

CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html)
 
-## Unreleased (0.4.0)
+## [0.4.0] 2023-03-21
 
 ### Added