Configure Dependabot for GitHub Actions

[ccjernigan]

Is your feature request related to a problem? Please describe.

We don't have a reliable way to detect when GitHub Actions have new versions

Describe the solution you'd like

Configure .github/dependabot.yml file with the following

version: 2
updates:
  - package-ecosystem: "github-actions"
    directory: "/"
    schedule:
      interval: "daily"

You can see an example in context here: https://github.com/zcash/secant-android-wallet/blob/main/.github/dependabot.yml