Support vulnerability-alerts permission

[ayetealab]

Summary

GitHub Actions now documents vulnerability-alerts as a valid permission scope with read and none access levels. actionlint needs to be updated to support this scope. Please also review pull request: #658

Changes

• Adds support for the vulnerability-alerts GitHub Actions permission scope
• Allow read and none, and reject write
• Update permission fixtures and checks documentation output

Testing

• make build
• go test ./...
• make lint