[MAINT] Github Actions Reunification - `dependabot.yml`

[damienwebdev]

There are many actions / workflows on very stale versions. We should update these and maintain them with dependabot.

We need something like:

version: 2
updates:
  # Maintain dependencies for GitHub Actions
  - package-ecosystem: "github-actions"
    directory: "/"
    schedule:
      interval: "weekly"
  - package-ecosystem: "npm"
    directory: "/"
    schedule:
      interval: "weekly"