Update dependencies from https://github.com/dotnet/arcade build 20210812.1 (#35379)

Microsoft.DotNet.Build.Tasks.Templating , Microsoft.DotNet.Build.Tasks.Installers , Microsoft.DotNet.Arcade.Sdk , Microsoft.DotNet.Helix.Sdk
 From Version 6.0.0-beta.21406.6 -> To Version 6.0.0-beta.21412.1

Co-authored-by: dotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>