.Net: Fix BaseTest (#12208)

### Motivation and Context

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We are seeing exceptions in some samples due to a bug in the
`BaseTest.cs` module, that ignores the `modelName` parameter when
creating a kernel with chat completion.

### Description

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These notes will help understanding how your code works. Thanks! -->
This PR ensures that the `modelName` parameter is consistently passed to
the `AddChatCompletionToKernel` method.

### Contribution Checklist

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- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
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raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

Author: TaoChenOSU

dotnet/src/InternalUtilities/samples/InternalUtilities/BaseTest.cs

@@ -50,21 +50,20 @@ public abstract class BaseTest : TextWriter
     protected bool UseBingSearch => TestConfiguration.Bing.ApiKey is not null;
 
     protected Kernel CreateKernelWithChatCompletion(string? modelName = null)
-        => this.CreateKernelWithChatCompletion(useChatClient: false, out _);
+        => this.CreateKernelWithChatCompletion(useChatClient: false, out _, modelName);
 
     protected Kernel CreateKernelWithChatCompletion(bool useChatClient, out IChatClient? chatClient, string? modelName = null)
     {
         var builder = Kernel.CreateBuilder();
 
-        AddChatCompletionToKernel(builder, modelName);
         if (useChatClient)
         {
             chatClient = AddChatClientToKernel(builder);
         }
         else
         {
             chatClient = null;
-            AddChatCompletionToKernel(builder);
+            AddChatCompletionToKernel(builder, modelName);
         }
 
         return builder.Build();