feat: bump to runtime to Node 24

[peterdeme]

I have added a breaking change footer in the commit message so in theory this'll automatically bump a major on merge. 🙂

Addresses #55

The following warning is seen when running v1.23.0 version of the action. The action will be forced to use node24 starting June 2nd, 2026.

Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: spacelift-io/setup-spacectl@ff220d63d9e7649d6aa542cf2629269b6dd74f0f. 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/