Update dependabot.yaml

[pamelafox]

Purpose

This pull request introduces a change to the .github/dependabot.yaml file. The change adds a new package ecosystem for GitHub Actions to the Dependabot configuration, which is set to check for updates on a weekly basis. This means Dependabot will now also check for updates to GitHub Actions used in the repository every week.

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe: