ci: fix excessive GitHub workflow token permissions

[gaganhr94]

Summary

The OpenSSF Scorecard Token-Permissions check flags GitHub Actions workflows in this repository that do not restrict the default GITHUB_TOKEN permissions.

Scorecard Warning

Warn: no topLevel permission defined: .github/workflows/antithesis-verify.yml:1

Proposed Fix

Add permissions: contents: read at the workflow level in antithesis-verify.yml. This follows the principle of least privilege and restricts the token to only reading repository contents.

Impact

• Improves the OpenSSF Scorecard Token-Permissions score
• Follows security best practices by applying the principle of least privilege to CI/CD tokens
• No functional impact — the workflow only checks out code and runs Docker builds locally

References

• OpenSSF Scorecard Token-Permissions check
• GitHub Actions: Setting permissions