build: add 'github-actions' to dependabot setting (#4)

.github/dependabot.yml

@@ -1,11 +1,10 @@
-# To get started with Dependabot version updates, you'll need to specify which
-# package ecosystems to update and where the package manifests are located.
-# Please see the documentation for all configuration options:
-# https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
-
 version: 2
 updates:
-  - package-ecosystem: "composer" # See documentation for possible values
-    directory: "/" # Location of package manifests
+  - package-ecosystem: "composer"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+  - package-ecosystem: "github-actions"
+    directory: "/"
     schedule:
       interval: "weekly"