CHANGELOG.md: add release date

Author: tarcieri

dbl/CHANGELOG.md

@@ -4,7 +4,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## 0.4.0
+## 0.4.0 (2025-08-04)
 ### Changed
 - Migrated from `generic-array` to `hybrid-array` ([#944])
 - Edition changed to 2024 and MSRV bumped to 1.85 ([#1149])