.NET: Cannot reuse Workflow with shared Executor instances that do not implement IResettableExecutor

[TaoChenOSU]

• Sample: https://github.com/microsoft/agent-framework/tree/main/dotnet/samples/GettingStarted/Workflows/Agents/WorkflowAsAnAgent
• Detail: Running the sample linked above will result in exception InvalidOperationException("Cannot reuse Workflow with shared Executor instances that do not implement IResettableExecutor."); when the conversation exceeds one turn.