Updated changelog

com.unity.render-pipelines.high-definition/CHANGELOG.md

 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [unreleased]
-
+- Fixed an issue with PreIntegratedFGD texture being sometimes destroyed and not regenerated causing rendering to break
 
 ## [3.0.0-preview]