Fix: missing redis pvc storageclass in helm (#6788)

fix redis pvc in helm deployment

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

helm/templates/redis.yaml

     {{- include "ragflow.labels" . | nindent 4 }}
     app.kubernetes.io/component: redis
 spec:
+  {{- with .Values.redis.storage.className }}
+  storageClassName: {{ . }}
+  {{- end }}
   accessModes:
     - ReadWriteOnce
   resources: