Use dependabot for bumping versions

[scottyhq]

https://github.blog/2023-01-12-a-smarter-quieter-dependabot/

because github actions go out of date eventually with deprecation messages:

https://github.com/snowex-hackweek/agu_splashpage/actions/runs/7670480012

The following actions uses node12 which is deprecated and will be forced to run on node16: nwtgck/actions-netlify@v1.2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, actions/cache@v3, conda-incubator/setup-miniconda@v2, nwtgck/actions-netlify@v1.2. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.