ci: Include workflow files in dependabot

Signed-off-by: Jun Xiang <[email protected]>

.github/dependabot.yml

@@ -5,6 +5,12 @@
 
 version: 2
 updates:
+  - package-ecosystem: "github-actions"
+    # Workflow files stored in the default location of `.github/workflows`. (You don't need to specify `/.github/workflows` for `directory`. You can use `directory: "/"`.)
+    directory: "/"
+    schedule:
+      interval: "weekly"
+
   - package-ecosystem: "npm" # See documentation for possible values
     directory: "/" # Location of package manifests
     schedule: