update changelog

Author: pfefferle

CHANGELOG.md

@@ -1120,6 +1120,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * initial
 
+[Unreleased]: https://github.com/Automattic/wordpress-activitypub/compare/4.3.0...trunk
+<!-- Add new release below and update "Unreleased" link -->
 [4.3.0]: https://github.com/Automattic/wordpress-activitypub/compare/4.2.1...4.3.0
 [4.2.1]: https://github.com/Automattic/wordpress-activitypub/compare/4.2.0...4.2.1
 [4.2.0]: https://github.com/Automattic/wordpress-activitypub/compare/4.1.1...4.2.0