Use File::Copy::Recursive instead of File::Copy in tools/signing/nightly/sign-nightly to move directories

In tools/signing/nightly/sign-nightly there are two places where we use the move function from File::Copy to move directories. However File::Copy is not supposed to be able to move directories, only single files. It only works by chance if the source and destinations are on the same filesystem and a rename is working. We should use File::Copy::Recursive instead.