CI: Use Windows Containers in CI when possible

[bruno-garcia]

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We have a 'desktop' step on Windows that installs Unity and it's rather slow. Ideally we use this image instead: https://hub.docker.com/layers/editor/unityci/editor/windows-2021.3.2f1-windows-il2cpp-1.0.1/images/sha256-f47eb164cb4cd8e1b1f0100975a941a70095ab824ea7d7233dee639b5cba5385?context=explore