Add `Serializable` attribute to `AdditionalEmailSendingArgs`.

framework/src/Volo.Abp.Emailing/Volo/Abp/Emailing/AdditionalEmailSendingArgs.cs

@@ -1,8 +1,10 @@
+using System;
 using System.Collections.Generic;
 using Volo.Abp.Data;
 
 namespace Volo.Abp.Emailing;
 
+[Serializable]
 public class AdditionalEmailSendingArgs
 {
     public List<string>? CC { get; set; }