feat: providing a public accessor for the NetworkBehaviour of a NetworkVariableBase (#2367)

Author: jeffreyrainy

com.unity.netcode.gameobjects/Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -18,6 +18,11 @@ public abstract class NetworkVariableBase : IDisposable
         /// </summary>
         private protected NetworkBehaviour m_NetworkBehaviour;
 
+        public NetworkBehaviour GetBehaviour()
+        {
+            return m_NetworkBehaviour;
+        }
+
         /// <summary>
         /// Initializes the NetworkVariable
         /// </summary>