Update GitHub actions, Node.js 20 deprecated

[troglobit]

The CI builds have started warning about the deprecation of older GitHub actions. See for example https://github.com/kernelkit/infix/actions/runs/22944273787:

"Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: actions/cache@v4, actions/checkout@v4, actions/upload-artifact@v4. Actions will be forced to run with Node.js 24 by default starting June 2nd, 2026. Please check if updated versions of these actions are available that support Node.js 24. To opt into Node.js 24 now, set the FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true environment variable on the runner or in your workflow file. Once Node.js 24 becomes the default, you can temporarily opt out by setting ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Reviewing the release notes of one of the actions revealed this nugget:

Important

actions/cache@v5 runs on the Node.js 24 runtime and requires a minimum Actions Runner > version of 2.327.1.

If you are using self-hosted runners, ensure they are updated before upgrading.