Bump node version from 20 to 24

[dncrews]

Hey @punkle I hope it's OK that I brought this to you. This resolves the following issue all of the actions' customers are now having, and I'm hoping we can get 0.6.0 (or maybe 1.0.0?) out ASAP, ahead of the GH mandate:

Validations / Backstage Validation / Backstage Validation
Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: RoadieHQ/backstage-entity-validator@v0.5.0. 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/

I believe I saw that there are tests throughout that ensure functionality in Node24, so I didn't have any major concerns, but I'm not super familiar with this codebase yet, so I could be wrong.