Configure Dependabot to check for outdated actions used in workflows

Dependabot will periodically check the versions of all actions used in the repository's workflows. If any are found to
be outdated, it will submit a pull request to update them.
NOTE: Dependabot's PRs will sometimes try to pin to the patch version of the action (e.g., updating `uses: foo/bar@v1`
to `uses: foo/bar@v2.3.4`). When the action author has provided a major version ref, use that instead
(e.g., `uses: foo/bar@v2`). Dependabot will automatically close its PR once the workflow has been updated.
More information:
https://docs.github.com/en/github/administering-a-repository/keeping-your-actions-up-to-date-with-dependabot

.github/dependabot.yml

+# See: https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates#about-the-dependabotyml-file
+version: 2
+
+updates:
+  # Configure check for outdated GitHub Actions actions in workflows.
+  # See: https://docs.github.com/en/github/administering-a-repository/keeping-your-actions-up-to-date-with-dependabot
+  - package-ecosystem: github-actions
+    directory: / # Check the repository's workflows under /.github/workflows/
+    schedule:
+      interval: daily