update changelog with unreleased section

Author: graingert-coef

CHANGELOG.md

@@ -2,6 +2,12 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## [UNRELEASED]
+
+## Changed
+
+- [#2734](https://github.com/plotly/dash/pull/2734) Configure CI for Python 3.10 [#1863](https://github.com/plotly/dash/issues/1863)
+
 ## [2.15.0] - 2024-01-31
 
 ## Added
@@ -19,7 +25,6 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## Changed
 - [#2652](https://github.com/plotly/dash/pull/2652) dcc.Clipboard supports htm_content and triggers a copy to clipboard when n_clicks are changed
 - [#2721](https://github.com/plotly/dash/pull/2721) Remove ansi2html, fixes [#2613](https://github.com/plotly/dash/issues/2713)
-- [#2734](https://github.com/plotly/dash/pull/2734) Configure CI for Python 3.10 [#1863](https://github.com/plotly/dash/issues/1863)
 
 ## [2.14.2] - 2023-11-27