test fix

Possible fix for what seems to be a timing related issue where not destroying the source prefab NetworkObject/GameObject it could cause an exception to occur.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformTests.cs

@@ -945,6 +945,7 @@ protected override IEnumerator OnTearDown()
         {
             m_EnableVerboseDebug = false;
             Object.DestroyImmediate(m_PlayerPrefab);
+            Object.DestroyImmediate(m_ChildObjectToBeParented);
             yield return base.OnTearDown();
         }
     }