ci: add Dependabot updates for GitHub Actions - #453

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@28c7f3d2b5162b5ddd3dfd9a45aa55eaf396478b, actions/setup-python@0f07f7f756721ebd886c2462646a35f78a8bc4de. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/