Configure Dependabot to check for outdated actions used in workflows (#19)

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be outdated, it will submit a pull request to update them.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 occasionally propose to pin to the patch version of the action (e.g., updating
`uses: foo/bar@v1` to `uses: foo/[email protected]`). 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

Author: per1234

.github/dependabot.yml

@@ -0,0 +1,13 @@
+# See: https://docs.github.com/en/code-security/supply-chain-security/configuration-options-for-dependency-updates#about-the-dependabotyml-file
+version: 2
+
+updates:
+  # Configure check for outdated GitHub Actions actions in workflows.
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/dependabot/README.md
+  # See: https://docs.github.com/en/code-security/supply-chain-security/keeping-your-actions-up-to-date-with-dependabot
+  - package-ecosystem: github-actions
+    directory: / # Check the repository's workflows under /.github/workflows/
+    schedule:
+      interval: daily
+    labels:
+      - "topic: infrastructure"