Let Dependabot update dependencies

[reneleonhardt]

Can Dependabot be enabled to update dependencies and GitHub Actions?

https://www.npmjs.com/package/@actions/core/v/1.8.0
is 4 years old for example.

https://github.com/reproducible-containers/buildkit-cache-dance/blob/v3.3.0/package.json#L36