Fix TSQLlint warnings in MSSQL test script

test/docker/db/mssql/initdb/initdb_mssql.sql

@@ -1,8 +1,16 @@
-USE [master]
+SET ANSI_NULLS ON;
+SET NOCOUNT ON;
+SET QUOTED_IDENTIFIER ON;
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+
+USE [master];
 GO
 
+-- prevent creation when already exists
 IF DB_ID('ejabberd_test') IS NOT NULL
-  set noexec on               -- prevent creation when already exists
+BEGIN
+SET NOEXEC ON;
+END
 
 CREATE DATABASE ejabberd_test;
 GO