Fix EXDEV: cross-device link not permitted error on latest version of cache-server

[KarthikHolikatti]

Hi @LouisHaftmann , after updating the server to the latest version i am facing following error:

code: 'EXDEV',
    syscall: 'rename',
    path: '/tmp/github-actions-cache-servercObiko/output',
    dest: '.data/storage/filesystem/gh-actions-cache/2a1b71173ab4a54104d53c483df9d50fe6ff7ced'

To fix this, i am proposing following changes, Please review:
#138