ci: add artifact-metadata permission for attestation storage records

Fixes warning: "Failed to create storage record: artifact-metadata:write
permission has been included"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/docker-publish.yml

@@ -33,6 +33,7 @@ permissions:
   packages: write
   id-token: write
   attestations: write
+  artifact-metadata: write
 
 concurrency:
   group: docker-${{ github.ref }}