(HHH-11456) SequenceHiLoGeneratorTest fails due to wrong select string on mssql

Mssql database has sys.sequences table. However test run this statement that causes failures when db is case-sensitive.

SELECT CONVERT(varchar(200), Current_value) FROM SYS.Sequences WHERE name

Moreover if this fails, the test leaks an open session. this causes problems if the database is configured so that a user can login only once at a time, because subsequent tests are unable to login.