Enable dependabot for github action updates

Author: tobiasdiez

.github/dependabot.yml

@@ -0,0 +1,10 @@
+# Documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"