Fix SQL Server tests

The repository 'microsoft/mssql-server-linux' is no longer maintained and container image cannot be pulled.
'mcr.microsoft.com/mssql/server' should be used instead.

See https://cloudblogs.microsoft.com/sqlserver/2021/05/20/microsoft-sql-server-linux-based-container-images-to-be-available-only-from-the-microsoft-container-registry/ for details.

Author: SergiiKram

test/WorkflowCore.Tests.SqlServer/DockerSetup.cs

@@ -11,7 +11,7 @@ public class SqlDockerSetup : DockerSetup
         public static string ConnectionString { get; set; }
         public static string ScenarioConnectionString { get; set; }
 
-        public override string ImageName => "microsoft/mssql-server-linux";
+        public override string ImageName => "mcr.microsoft.com/mssql/server";
         public override int InternalPort => 1433;
         public override TimeSpan TimeOut => TimeSpan.FromSeconds(120);