fix: Update for the new AgentRunResponseUpdate merge logic

AIAgent always sends out List<ChatMessage> now.

Author: lokitoth

dotnet/samples/GettingStarted/Workflows/Agents/WorkflowAsAnAgent/WorkflowFactory.cs

@@ -42,7 +42,7 @@ private static ChatClientAgent GetLanguageAgent(string targetLanguage, IChatClie
     /// Executor that aggregates the results from the concurrent agents.
     /// </summary>
     private sealed class ConcurrentAggregationExecutor() :
-        Executor<ChatMessage>("ConcurrentAggregationExecutor"), IResettableExecutor
+        Executor<List<ChatMessage>>("ConcurrentAggregationExecutor"), IResettableExecutor
     {
         private readonly List<ChatMessage> _messages = [];
 
@@ -53,9 +53,9 @@ private sealed class ConcurrentAggregationExecutor() :
         /// <param name="context">Workflow context for accessing workflow services and adding events</param>
         /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests.
         /// The default is <see cref="CancellationToken.None"/>.</param>
-        public override async ValueTask HandleAsync(ChatMessage message, IWorkflowContext context, CancellationToken cancellationToken = default)
+        public override async ValueTask HandleAsync(List<ChatMessage> message, IWorkflowContext context, CancellationToken cancellationToken = default)
         {
-            this._messages.Add(message);
+            this._messages.AddRange(message);
 
             if (this._messages.Count == 2)
             {