Fix property accessibility

sdk/iot/Azure.Iot.Hub.Service/src/Customized/Models/DigitalTwinInterfaces.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System.Collections.Generic;
+
+namespace Azure.Iot.Hub.Service.Models
+{
+    /// <summary>
+    /// The DigitalTwinInterfaces.
+    /// </summary>
+    public partial class DigitalTwinInterfaces
+    {
+        /// <summary>
+        /// Interface(s) data on the digital twin.
+        /// </summary>
+        internal IReadOnlyDictionary<string, PnpInterface> Interfaces { get; }
+    }
+}