docs(changelog): add screenshot strategy serialization to unreleased

Author: markushi

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Improvements
 
 - Fallback to distinct-id as user.id logging attribute when user is not set ([#4847](https://github.com/getsentry/sentry-java/pull/4847))
+- Session Replay: Add screenshot strategy serialization to RRWeb events ([#4851](https://github.com/getsentry/sentry-java/pull/4851))
 
 ## 8.25.0