update changelog

Author: JulianAtkins

user_guide_src/source/changelogs/v4.8.0.rst

@@ -174,6 +174,7 @@ Libraries
 =========
 
 - **Context**: This new feature allows you to easily set and retrieve normal or hidden contextual data for the current request. See :ref:`Context <context>` for details.
+- **Images:**: Added support for the AVIF file format.
 
 Helpers and Functions
 =====================