Update dependabot.yaml for GitHub actions

[pamelafox]

Purpose

This pull request includes a change to the .github/dependabot.yaml file. The change adds a new github-actions package ecosystem and sets a weekly update schedule for it.

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: