CI matrix change: add Windows.Server.Core.20H2 - Second attempt (dotnet#60054)

* CI matrix change: add Windows.Server.Core.20H2 (dotnet#59572)

* Add Windows.Server.Core.20H2 to CI matrix

* add windows server 20H2

* Remove 20H2 from PR

* Remove 20H2 from PR run

* change helix queue for Windows.Server.Core.20H2

Author: Jan Jahoda

eng/pipelines/libraries/helix-queues-setup.yml

@@ -132,9 +132,11 @@ jobs:
             - Windows.81.Amd64.Open
             - Windows.10.Amd64.ServerRS5.Open
             - Windows.10.Amd64.Server19H1.Open
+            - Windows.10.Amd64.Server20H2.Open
             - ${{ if ne(parameters.jobParameters.runtimeFlavor, 'mono') }}:
               - (Windows.Nano.1809.Amd64.Open)[email protected]/dotnet-buildtools/prereqs:nanoserver-1809-helix-amd64-08e8e40-20200107182504
               - (Windows.Server.Core.1909.Amd64.Open)[email protected]/dotnet-buildtools/prereqs:windowsservercore-2004-helix-amd64-20200904200251-272704c
+              - (Windows.Server.Core.20H2.Amd64.Open)[email protected]/dotnet-buildtools/prereqs:windowsservercore-20H2-helix-amd64-20210922171304-edc3733
           - ${{ if ne(parameters.jobParameters.isFullMatrix, true) }}:
             - Windows.81.Amd64.Open
             - Windows.10.Amd64.Server19H1.ES.Open