e2e: seed node image with skopeo to preserve its digest

GitHub moved the ubuntu-latest runner from Ubuntu 24.04 to 26.04,
which upgraded podman from 4.9.3 to 5.7.0. Since then most of the
bink e2e tests fail on every Kubernetes version with:

    Value for field 'Booted' failed to satisfy matcher.
    Value for field 'ImageDigest' failed to satisfy matcher.
    Expected "...a256:9566a5..." to equal "...a256:0136fd..."

seed-node-image pulls the bootc image that the node disk image was
installed from (by digest) and re-pushes it to the local bink
registry with `podman push`. The tests take the "original" digest
from the local registry (E2E_NODE_IMAGE_DIGEST) and expect the
node's booted digest to match it.

podman 4 pushed the OCI manifest unchanged, so both digests were
sha256:9566a5.... podman 5 rewrites the manifest on push, so the
local registry now holds sha256:0136fd... while the VM is still
booted from sha256:9566a5.... Every test that checks the booted
digest against the original image now times out. Tests that only
check the update images still pass, because those images are built
and pushed locally and their digests are read back from the
registry.

Copy the image directly from the source registry to the local
registry with `skopeo copy --preserve-digests` so the manifest is
transferred unchanged, independent of the podman version on the
runner. The local podman tag is kept because build-update-image
builds FROM localhost:5000/node:latest.

Assisted-by: AI
Signed-off-by: Alice Frosi <afrosi@redhat.com>

Author: alicefr

Makefile

@@ -228,15 +228,19 @@ undeploy: kustomize ## Undeploy controller from the K8s cluster specified in ~/.
 # Note the :latest tag here: this makes the pull policy be Always.
 IMG_BINK ?= registry.cluster.local:5000/bootc-operator-e2e:latest
 
+# Copy with skopeo rather than `podman push`: the node disk image booted the
+# source digest, and podman 5 rewrites the manifest on push, which changes it.
 .PHONY: seed-node-image
 seed-node-image: ## Pull the bootc node image by digest and push to the bink registry.
 	bink registry start
 	podman pull $(BINK_NODE_DISK_IMAGE)
 	bootc_img=$$(podman inspect --format '{{index .Config.Labels "bink.bootc-image"}}' $(BINK_NODE_DISK_IMAGE)) && \
 		bootc_digest=$$(podman inspect --format '{{index .Config.Labels "bink.bootc-image-digest"}}' $(BINK_NODE_DISK_IMAGE)) && \
 		podman pull "$$bootc_img@$$bootc_digest" && \
-		podman tag "$$bootc_img@$$bootc_digest" localhost:5000/node:latest
-	podman push --tls-verify=false localhost:5000/node:latest
+		podman tag "$$bootc_img@$$bootc_digest" localhost:5000/node:latest && \
+		bootc_repo=$${bootc_img%:*} && \
+		skopeo copy --preserve-digests --dest-tls-verify=false \
+			"docker://$$bootc_repo@$$bootc_digest" docker://localhost:5000/node:latest
 
 .PHONY: start-bink
 start-bink: seed-node-image ## Start a bink cluster (idempotent).