update CHANGELOG for 3.9.0

Author: kevinAlbs

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](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## 3.9.0 [Unreleased]
+## 3.9.0
 
 ### Added