testing light gbm tests sequentially (#6968)

test/Microsoft.ML.TestFramework/BaseTestClass.cs

@@ -81,7 +81,7 @@ namespace Microsoft.ML.TestFramework
             Cleanup();
             Process proc = Process.GetCurrentProcess();
             Console.WriteLine($"Finished test: {FullTestName} " +
-                $"with memory usage {proc.WorkingSet64.ToString("N", CultureInfo.InvariantCulture)}");
+                $"with memory usage {proc.WorkingSet64.ToString("N", CultureInfo.InvariantCulture)} and max memory usage {proc.PeakWorkingSet64.ToString("N", CultureInfo.InvariantCulture)}");
         }
 
         protected virtual void Initialize()

test/Microsoft.ML.Tests/TrainerEstimators/TreeEstimators.cs

@@ -24,6 +24,10 @@ using System.IO;
 
 namespace Microsoft.ML.Tests.TrainerEstimators
 {
+    [CollectionDefinition(nameof(NoParallelizationDefinition), DisableParallelization = true)]
+    public class NoParallelizationDefinition { }
+
+    [Collection(nameof(NoParallelizationDefinition))]
     public partial class TrainerEstimators : TestDataPipeBase
     {
         /// <summary>