#673 [tests][mutants] 変異試験が防御を外したまま kill(-1) などを実行し、利用者の全プロセスを止める - #678

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4, actions/setup-python@v5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/