use `CONIN$` instead of `/dev/tty` on windows — heartwood

This allows git-remote-rad to succesfully launch an editor on windows

                 .write(true)
                 .open("/dev/tty")?;
             process::Stdio::from(tty)
         } else if cfg!(windows) {
             let tty = fs::OpenOptions::new()
                 .read(true)
                 .open("CONIN$")?;
             process::Stdio::from(tty)
         } else {
             return Err(io::Error::new(
                 io::ErrorKind::Unsupported,