Test backup: add volumesnapshot annotation

velero/test-backup.yaml

@@ -2,6 +2,8 @@ apiVersion: velero.io/v1
 kind: Schedule
 metadata:
   name: test-backup
+  annotations:
+    velero.io/csi-volumesnapshot-class_driver.longhorn.io: "longhorn-backup-vsc"
 spec:
   schedule: "*/2 * * * *"  # Daily at 1 AM
   template: