I would like to cache various files created by the root user during my build. This would allow me to cache Docker steps as well as files downloaded by a different user, see https://github.com/jyn514/docs.rs/runs/349254873#step:18:1 for an example.

Currently this fails with an error from tar:

/bin/tar: ./overlay2: Cannot open: Permission denied
/bin/tar: ./builder: Cannot open: Permission denied
...
/bin/tar: Exiting with failure status due to previous errors

As a workaround, I could probably make the files world-readable, but I have a feeling that they will not be owned by the right user if the cache is hit.