Similar to
https://github.com/rclone/rclone/commit/acf1e2df84a350b7a86d7672d749dfb1ba090a44,
go1.21.4 appears to have broken sync.MoveDir on Windows because
filepath.VolumeName() returns `\\?` instead of `\\?\C:` in cleanRootPath. It
looks like the Go team is aware of the issue and planning a fix, so this may
only be needed temporarily.