.NET Workflows - Remove empty message injection in declarative workflow agent provider. (#3819)

* Fixed

* Update test-case expectations

dotnet/src/Microsoft.Agents.AI.Workflows.Declarative.AzureAI/AzureAgentProvider.cs

@@ -123,7 +123,7 @@ public sealed class AzureAgentProvider(Uri projectEndpoint, TokenCredential proj
         IAsyncEnumerable<AgentResponseUpdate> agentResponse =
             messages is not null ?
                 agent.RunStreamingAsync([.. messages], null, runOptions, cancellationToken) :
-                agent.RunStreamingAsync([new ChatMessage(ChatRole.User, string.Empty)], null, runOptions, cancellationToken);
+                agent.RunStreamingAsync([], null, runOptions, cancellationToken);
 
         await foreach (AgentResponseUpdate update in agentResponse.ConfigureAwait(false))
         {

dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/Testcases/InputArguments.json

@@ -10,7 +10,6 @@
     "conversation_count": 1,
     "min_action_count": 1,
     "min_response_count": 1,
-    "min_message_count": 2,
     "actions": {
       "start": [
         "invoke_poem"

dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/Testcases/Marketing.json

@@ -10,7 +10,6 @@
     "conversation_count": 1,
     "min_action_count": 3,
     "min_response_count": 3,
-    "min_message_count": 6,
     "actions": {
       "start": [
         "invoke_analyst",