GitHub Action: fails to push Docker image without tag

[sgerrand]

Error message from building a git tag:

/usr/bin/docker buildx build . \
  --iidfile /home/runner/work/_temp/docker-actions-toolkit-G9AUmT/build-iidfile-d3c407ba44.txt \
  --label org.opencontainers.image.created=2024-07-01T15:47:34.411Z \
  --label org.opencontainers.image.description=Alpine Linux package builder in Docker \
  --label org.opencontainers.image.licenses= \
  --label org.opencontainers.image.revision=8da63dc3a1f5d59e2be146c110d28717700e2b4f \
  --label org.opencontainers.image.source=https://github.com/sgerrand/docker-alpine-abuild \
  --label org.opencontainers.image.title=docker-alpine-abuild \
  --label org.opencontainers.image.url=https://github.com/sgerrand/docker-alpine-abuild \
  --label org.opencontainers.image.version= \
  --platform linux/amd64,linux/arm/v7,linux/arm64 \
  --attest type=provenance,mode=max,builder-id=https://github.com/sgerrand/docker-alpine-abuild/actions/runs/9747257041/attempts/1 \
  --metadata-file /home/runner/work/_temp/docker-actions-toolkit-G9AUmT/build-metadata-9c7cb11687.json \
  --push
ERROR: tag is needed when pushing to registry

Looks like the git tag reference doesn't get passed to the build job which then causes a failure when docker buildx build attempts to push the freshly built image.