Update buildx config to use the correct docker driver

This PR fixes a configuration bug in docker buildx Action that was causing Cog to attempt to pull built images from a remote registry rather than the local build.

This release is tagged as v2.0.2, but it also updates the broader v2 major version tag.

To use this version:

- name: Setup Cog
  uses: replicate/setup-cog@v2

See #39

Thanks to @one1zero1one and @Theodotus1243 for debugging this! 🙏🏼