Restrict #2218 tests to only dialects that are supported

Author: hazzik

src/NHibernate.Test/Async/NHSpecificTest/NH2951/Fixture.cs

@@ -18,6 +18,11 @@ namespace NHibernate.Test.NHSpecificTest.NH2951
 	[TestFixture]
 	public class FixtureAsync : BugTestCase
 	{
+		protected override bool AppliesTo(Dialect.Dialect dialect)
+		{
+			return dialect.SupportsScalarSubSelects;
+		}
+
 		protected override void OnTearDown()
 		{
 			using (ISession session = OpenSession())

src/NHibernate.Test/NHSpecificTest/NH2951/Fixture.cs

@@ -7,6 +7,11 @@ namespace NHibernate.Test.NHSpecificTest.NH2951
 	[TestFixture]
 	public class Fixture : BugTestCase
 	{
+		protected override bool AppliesTo(Dialect.Dialect dialect)
+		{
+			return dialect.SupportsScalarSubSelects;
+		}
+
 		protected override void OnTearDown()
 		{
 			using (ISession session = OpenSession())