fix(ci): checkout staging branch in deploy-staging workflow

The workflow_run trigger runs on the default branch (main), but we need
to deploy code from the staging branch.

Author: zainfathoni

.github/workflows/deploy-staging.yml

@@ -28,6 +28,8 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
+        with:
+          ref: staging
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3