Merge pull request #23 from ranocha/hr/dependabot

enable dependabot for GitHub actions

.github/dependabot.yml

+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"