fix: add attestations write permission to workflow

The artifact attestation step was failing with:
"Resource not accessible by integration"

Added missing attestations: write permission to fix the issue.

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

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

.github/workflows/docker-publish.yml

@@ -22,6 +22,7 @@ jobs:
       contents: read
       packages: write
       id-token: write
+      attestations: write
 
     steps:
       - name: Checkout repository