When we attempt to resolve the executable for Codecov, we used to also resolve to codecov.exe. This was fine when the executable used was the Codecov exe project, but now that the only way forward is to use the official binary from Codecov, the exe variant will only run on Windows.

As such, we should only resolve to the exe when running on Windows, but not on any of the unix platforms.

This is mainly a fallback, so it won't be as noticable by existing usage that uses Cake.Codecov v1.1.0.