Add GitHub actions to dependabot config

Author: jasonjoh

.github/dependabot.yml

@@ -1,6 +1,10 @@
 version: 2
 updates:
-  - package-ecosystem: "bundler" # See documentation for possible values
-    directory: "graph-sample/" # Location of package manifests
+  - package-ecosystem: bundler # See documentation for possible values
+    directory: graph-sample/ # Location of package manifests
     schedule:
-      interval: "weekly"
+      interval: weekly
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly