ci: fix semgrep 1.99 CLI drift - #4

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, github/codeql-action/analyze@v3, github/codeql-action/init@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/