add changelog entry

Author: KoolADE85

CHANGELOG.md

@@ -2,6 +2,11 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## [UNRELEASED]
+
+## Added
+- [#3440](https://github.com/plotly/dash/pull/3440) Modernize dcc.Dropdown
+
 ## [4.0.0rc0] - 2025-09-11
 - [#3398](https://github.com/plotly/dash/pull/3398) Modernize dcc.Input
 - [#3414](https://github.com/plotly/dash/pull/3414) Modernize dcc.Slider