Update CHANGELOG.md

Author: PGrawe

CHANGELOG.md

@@ -9,6 +9,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#2043](https://github.com/plotly/dash/pull/2043) Fix bug 
 [#2003](https://github.com/plotly/dash/issues/2003) in which 
 `dangerously_allow_html=True` + `mathjax=True` works in some cases, and in some cases not.
+- [#2047](https://github.com/plotly/dash/pull/2047) Fix bug [#1979](https://github.com/plotly/dash/issues/1979) in which `DASH_DEBUG` as enviroment variable gets ignored.
 
 ## [2.4.1] - 2022-05-11