COMP: Add Dependabot workflow to update GitHub Actions

References:
* https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
* https://docs.github.com/en/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot#enabling-dependabot-version-updates-for-actions

Author: jcfr

.github/dependabot.yml

@@ -0,0 +1,12 @@
+# Set update schedule for GitHub Actions
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "weekly"
+    commit-message:
+      # Prefix all commit messages with "COMP: "
+      prefix: "COMP"