Temp fix for the race condition during the tests. (#7021)

* temp fixing the race condition during the tests

* making db tests sequential

test/Microsoft.ML.Tests/DatabaseLoaderTests.cs

@@ -20,6 +20,9 @@ using Xunit.Abstractions;
 
 namespace Microsoft.ML.Tests
 {
+    [CollectionDefinition(nameof(NoParallelizationDefinition), DisableParallelization = true)]
+    public class NoParallelizationDefinition { }
+    [Collection(nameof(NoParallelizationDefinition))]
     public class DatabaseLoaderTests : BaseTestClass
     {
         public DatabaseLoaderTests(ITestOutputHelper output)

test/Microsoft.ML.Tests/Transformers/WordEmbeddingsTests.cs

@@ -12,6 +12,9 @@ using Xunit.Abstractions;
 
 namespace Microsoft.ML.Tests.Transformers
 {
+    [CollectionDefinition(nameof(NoParallelizationDefinition), DisableParallelization = true)]
+    public class NoParallelizationDefinition { }
+    [Collection(nameof(NoParallelizationDefinition))]
     public sealed class WordEmbeddingsTests : TestDataPipeBase
     {
         public WordEmbeddingsTests(ITestOutputHelper helper)