fix(issue-11): 敏感文件正则误报 key.js/cert.js/pem.js——限定独立扩展名匹配 - #18

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/