* ci(pjdfstest): cache docker layers via GHA to avoid apt mirror flakes
Replace the local buildx cache + manual fallback with docker/setup-buildx-action
and docker/build-push-action using type=gha cache. The e2e and pjdfstest Dockerfile
layers now persist across runs in GitHub's own cache backend, so apt-get update
only hits Ubuntu mirrors when the Dockerfiles change. Also add Acquire::Retries
and Timeout so first-run cache-miss builds survive transient mirror sync errors.
* ci(pjdfstest): use local registry to share e2e image across buildx builds
The docker-container buildx driver cannot see images loaded into the host
Docker daemon, so the second build's FROM chrislusf/seaweedfs:e2e failed with
"not found" on registry-1.docker.io.
Run a local registry:2 on the runner, push both images to localhost:5000,
remap the FROM via build-contexts so the Dockerfile stays unchanged, then
tag the pulled images locally for docker compose to consume.
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