Add PR-3358 changelog entry

Adding missing changelog entry for PR-3358.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -9,6 +9,8 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ## [Unreleased]
 
 ### Added
+
+- Added `NetworkManager.OnPreShutdown` which is called before the NetworkManager cleans up and shuts down. (#3358)
 - Added `FastBufferReader(ArraySegment<byte> buffer, Allocator copyAllocator)` constructor that uses the `ArraySegment.Offset` as the `FastBufferReader` offset and the `ArraySegment.Count` as the `FastBufferReader` length. (#3320)
 - Added `FastBufferReader(ArraySegment<byte> buffer, Allocator copyAllocator, int length = -1)` constructor that uses the `ArraySegment.Offset` as the `FastBufferReader` offset. (#3320)