Added new Unreleased section

Author: michalChrobot

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -6,6 +6,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).
 
+## [Unreleased]
+
+### Added
+
+### Fixed
+
+### Changed
+
 ## [1.13.0] - 2025-04-29
 
 ### Added