GHA: Add Windows

[dweindl]

Verify all tests pass on Windows

[fbergmann]

all that should be needed here would be to add the platform into the matrix like so:

strategy:
 matrix:
    platform: [windows-latest, macos-latest, ubuntu-latest]
runs-on: ${{ matrix.platform }}

in the worst case some of the tasks could be disabled on windows (no need to run codecoverage on all platforms i think), So some:

    if: matrix.platform == 'ubuntu-latest'

on those steps will ensure that they are only executed there.