Generate GitHub Artifact Attestations to install github-mcp-server securely.

https://docs.github.com/en/actions/security-for-github-actions/using-artifact-attestations/using-artifact-attestations-to-establish-provenance-for-builds

Now github-mcp-server doesn't generate attestations.

https://github.com/github/github-mcp-server/attestations

I'll send a pull request to resolve this issue: #174