Ignore test for Firebird 2.5

Author: alex-kulakov

Orm/Xtensive.Orm.Tests/Linq/SetOperationsTest.cs

@@ -96,6 +96,11 @@ from c in customers
     [Test]
     public void ConcatDifferentTest()
     {
+      if (StorageProviderInfo.Instance.CheckProviderIs(StorageProvider.Firebird)) {
+        //Firebird 2.5 has issues with same table united to self
+        Require.ProviderVersionAtLeast(StorageProviderVersion.Firebird30);
+      }
+
       var customers = Session.Query.All<Customer>();
       var employees = Session.Query.All<Employee>();
       var result = (