[DTLS 1.3] Prepare (D)TLS 1.2 implementation - #6001

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. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Input 'save-always' has been deprecated with message: save-always does not work as intended and will be removed in a future release. A separate `actions/cache/restore` step should be used instead. See https://github.com/actions/cache/tree/main/save#always-save-cache for more details.