Update CHANGELOG.md

Author: oleibman

CHANGELOG.md

@@ -35,6 +35,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 - Recognize application/x-empty mimetype. [Issue #4521](https://github.com/PHPOffice/PhpSpreadsheet/issues/4521) [PR #4524](https://github.com/PHPOffice/PhpSpreadsheet/pull/4524)
 - Micro-optimization in getSheetByName. [PR #4499](https://github.com/PHPOffice/PhpSpreadsheet/pull/4499)
 - Bug in resizeMatricesExtend. [Issue #4451](https://github.com/PHPOffice/PhpSpreadsheet/issues/4451) [PR #4474](https://github.com/PHPOffice/PhpSpreadsheet/pull/4474)
+- Allow Replace of Dummy Function with Custom Function. [PR #4544](https://github.com/PHPOffice/PhpSpreadsheet/pull/4544)
 
 ## 2025-06-22 - 4.4.0