Azure: Move to windows-2019

As per https://github.com/actions/virtual-environments/issues/4312

 the
Windows-2016 environments are scheduled for deprecation and removal in
early 2022.  Move to windows-2019 now to avoid this (Visual Studio 2019
is included here, hence the tag naming scheme change).

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>