CI: example image docker build failures

[vdice]

The docker build step for example images are failing (when in 'test' mode). See https://github.com/spinkube/containerd-shim-spin/actions/runs/7759094517/job/21162393271?pr=2 and https://github.com/spinkube/containerd-shim-spin/actions/runs/7759094517/job/21162393801?pr=2

Error snippet:

#13 importing to docker
#13 ERROR: cannot load wasi image on linux
------
 > exporting to docker image format:
------
------
 > importing to docker:
------
ERROR: failed to solve: rpc error: code = Unknown desc = cannot load wasi image on linux
Error: buildx failed with: ERROR: failed to solve: rpc error: code = Unknown desc = cannot load wasi image on linux

It almost seems like we'd need to switch the docker/build-push-action version back to v3 as we do when not in 'test' mode (https://github.com/spinkube/containerd-shim-spin/blob/main/.github/workflows/docker-build-push.yaml#L54-L56).

However, the corresponding workflow in deislabs/containerd-wasm-shims doesn't appear to hit the same error, so I'm confused (see for example https://github.com/deislabs/containerd-wasm-shims/actions/runs/7632914430/job/20794094653)

cc @Mossaka

[Mossaka]

Ummm that's strange

[Mossaka]

It doesn't seem like reverting back to v3 solves the problem (e.g. see this run)

[Mossaka]

Okay, it looks like containerd-wasm-shims hit the same issue; https://github.com/deislabs/containerd-wasm-shims/actions/runs/7763088430/job/21174661154?pr=204

[Mossaka]

The difference between the successful run and unsuccessful run:

containerd: 1.6.27 -> 1.6.28
runc: 1.1.11 -> 1.1.12
docker buildx: 0.11.2 -> 0.12.1

[Mossaka]

Related discussion: https://cloud-native.slack.com/archives/C04LTPB6Z0V/p1706919571842939

[Mossaka]

The solution is to enable containerd image store. See #9

[vdice]

👏 Thanks @Mossaka!