Docker 28+ defaults to the containerd image store, which pushes layers
uncompressed instead of gzip. The GHA runner image updated Docker to
29.x (actions/runner-images#13633), causing the `nixos/nix:2.33.3`
image to balloon from 138 MB to 505 MB, with all 70 layers pushed as
`application/vnd.docker.image.rootfs.diff.tar` instead of `.tar.gzip`.
OCI clients that only support gzip (e.g. `go-containerregistry`, used
by Concourse CI) fail with "gzip: invalid header".
This commit disables the containerd snapshotter in the release workflow
before any Docker operations, restoring the classic storage driver that
preserves gzip compression through the `docker load` / `docker push`
pipeline.
Fixes#15246
2ccb8a9a56