Enable automated updates for `Containerfile.dev` using Dependabot

[Dependabot](https://github.com/dependabot) is currently not configured to update the base image in the [`Containerfile.dev`](https://github.com/ericcornelissen/asdf-diffoci/blob/a84084bde852f05b355f5c02fcbf86a8054560f6/Containerfile.dev) because it does not support the file name. When Dependabot supports this file name, [its configuration](https://github.com/ericcornelissen/asdf-diffoci/blob/a84084bde852f05b355f5c02fcbf86a8054560f6/.github/dependabot.yml) should be updated to enable automated update for the base image.