(build) Pin to earlier Windows Build Image
(build) Pin to earlier Windows Build Image

Building of Chocolatey GUI hasn't been tested on anything other than
Visual Studio 2019, so let's stick with that for just now.  That is the
version of Visual Studio installed on the windows-2019 image.

gep13/ChocolateyGUI,gep13/ChocolateyGUI,gep13/ChocolateyGUI,gep13/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI,gep13/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI