fix: not using NativeArrayExtensions.IndexOf as this API changed in 21.0-pre.2 (#2303)

fix: not using NativeArrayExtensions.IndexOf as this API changed in 2.1.0-pre.2

Co-authored-by: ashwini <36935028+ashwinimurt@users.noreply.github.com>
Co-authored-by: Fatih Mar <mfatihmar@gmail.com>

com.unity.netcode.gameobjects/Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -413,7 +413,7 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public bool Contains(T item)
         {
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            int index = m_List.IndexOf(item);
             return index != -1;
         }
 
@@ -426,7 +426,7 @@ namespace Unity.Netcode
                 throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
             }
 
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            int index = m_List.IndexOf(item);
             if (index == -1)
             {
                 return false;