Dependabot configuration to update actions in workflow

[spatten]

Overview

Add a dependabot config to update github actions.

This PR contains a cherry-picked commit from https://github.com/fossas/fossa-action/pull/46

The original PR was provided by https://github.com/ScottBrenner. Thank you @ScottBrenner!

Checklist

~[ ] If I changed code, I ran yarn build and committed resulting changes.~ ~[ ] I added an example exercising this PRs functionality to .github/workflows/test.yml or explained why it doesn't make sense to do so.~