Secret scanning detects secrets in Actions logs [Public Preview]

### Value Prop
Secret scanning now detects secrets exposed in GitHub Actions workflow logs, closing a common and high-risk gap in your security coverage. When a token, API key, or credential surfaces in a log, GitHub will automatically open a secret scanning alert with additional information about the finding.

### Expected Outcome
Development teams need confidence that their automation pipelines are covered alongside their source code and GitHub surfaces. By extending secret scanning to Actions logs, developers can ship faster without worrying that their pipelines are silently leaking credentials.

This roadmap issue names no repository files, tests, or implementation entry points. Start by reviewing the secret-scanning and GitHub Actions documentation, then identify the product and engineering scope needed to detect credentials in workflow logs and create alerts with finding details.

索引モデルが issue の本文から書いたものです。