CI: Use 'windows-2019' image for Windows tests
CI: Use 'windows-2019' image for Windows tests

'windows-latest' is currently 'windows-2022'
with Visual Studio 2022.

Old versions of node-gyp don't know how to find Visual Studio 2022,
so the package build fails.

Switch back to 'windows-2019' with Visual Studio 2019,
which is supported by node-gyp 5.x, which apm still uses.

atom/github,atom/github,atom/github