fix: propagate real container exit code instead of hardcoding 0 - #7

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-go@v5, github/codeql-action/upload-sarif@ce64ddcb0d8d890d2df4a9d1c04ff297367dea2a. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/