Added missed line to changelog (#6029)

Update CHANGELOG.md

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - The capability to transfer a task from one project to another project has been disabled (<https://github.com/opencv/cvat/pull/5901>)
 - The bounding rectangle in the skeleton annotation is visible solely when the skeleton is active (<https://github.com/opencv/cvat/pull/5911>)
+- Base backend image upgraded from ubuntu:20.04 to ubuntu:22.04 (<https://github.com/opencv/cvat/pull/6021>)
 
 ### Deprecated
 - TDB