#2122 collapsed the per-registry builds into one build with two type=image
outputs and a single steps.build.outputs.digest. With build-push-action's
default provenance attestation, that digest does not resolve at ghcr, so the
multi-arch manifest step fails ("ghcr.io/...@sha256:...: not found"). Restore
the separate build-ghcr / build-dockerhub steps so each registry gets its own
digest. The ci-build.yml type=gha cache change from #2122 is kept.
Umputun
e575066ea9