Fix test harness casing and exclude test sources from app

GameList.Tests/Support/StubHttpClientFactory.cs

@@ -13,6 +13,6 @@ internal class StubHttpClientFactory : IHttpClientFactory
 
     public HttpClient CreateClient(string name)
     {
-        return new HttpClient(_handler, dispose: false);
+        return new HttpClient(_handler, disposeHandler: false);
     }
 }

GameList.Tests/Support/TestClientExtensions.cs

@@ -41,6 +41,6 @@ internal static class TestClientExtensions
 
         response.EnsureSuccessStatusCode();
         var json = await response.Content.ReadFromJsonAsync<JsonElement>();
-        return json.GetProperty("Id").GetInt32();
+        return json.GetProperty("id").GetInt32();
     }
 }