earthly buildkitd crash due to no space left on device on GHA

From log in https://github.com/neutronth/kpt-update-ksops-secrets/actions/runs/15002735417/job/42153645636?pr=52#step:3:4184. The earthly-buildkitd got crash due to no space left on device. :(

The workaround at the moment is to use `docker-unix-sock` option at the constructor level.