[io grant] Cover :parent arg in IO::Spec::Cygwin.canonpath
[io grant] Cover :parent arg in IO::Spec::Cygwin.canonpath

Rakudo impl: https://github.com/rakudo/rakudo/commit/0c8bef5a1e

bitrauser/roast,dogbert17/roast,perl6/roast,bitrauser/roast,dogbert17/roast