date changelog for 0.4.0 release

Author: ndgrigorian

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/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [dev] - YYYY-MM-DD
+## [0.4.0] - 2026-04-16
 ### Added
 * Added `patch_numpy_umath` and `restore_numpy_umath` functions for patching NumPy, and improved the patching implementation [gh-170](https://github.com/IntelPython/mkl_umath/pull/170)