Fix buildkit-cache-dance v3 API: replace deprecated cache-source with cache-map

[Copilot]

Summary

The buildkit-cache-dance v3.3.1 upgrade deprecated cache-source in favor of cache-map. Using the old input caused permission errors when the action attempted to create cache directories at system root paths like /var/cache/apk.

Why

Resolves Docker workflow build failures introduced by the buildkit-cache-dance major version bump.

What changed

• Replaced deprecated cache-source: go-build-cache with cache-map JSON mapping
• Mapped GitHub Actions cache subdirectories to Docker cache mount targets:
  • go-build-cache/apk → /var/cache/apk (Alpine packages)
  • go-build-cache/pkg → /go/pkg/mod (Go modules)
  • go-build-cache/build → /root/.cache/go-build (Go build artifacts)

MCP impact

• No tool or API changes

Prompts tested (tool changes only)

N/A

Security / limits

• No security or limits impact

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint - Not applicable (workflow YAML change only)
• Tested locally with ./script/test - Not applicable (workflow YAML change only)

Docs

• Not needed

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/reproducible-containers/buildkit-cache-dance/releases
  • Triggering command: /usr/bin/curl curl -s REDACTED (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[Copilot]

Pull request overview

Updates the Docker publish workflow to align with reproducible-containers/buildkit-cache-dance v3.x’s new input API, fixing CI build failures caused by the deprecated cache-source input.

Changes:

• Replaced cache-source with cache-map JSON mapping for buildkit-cache-dance v3.3.1.
• Mapped the existing go-build-cache/ Actions cache subdirectories to the intended BuildKit mount targets (/var/cache/apk, /go/pkg/mod, /root/.cache/go-build).