Toolbox setting persistence storage class to default does not work.

Summary

In our docs for persistence configuration, it states

If .storageClass is specified as ‘-‘, then the PersistentVolume will be created using the default StorageClass as specified in the Kubernetes cluster.

However, trying to set that does not set a storage class and leaves the pvc hanging in pending.
https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/charts/gitlab/charts/toolbox/templates/_helpers.tpl?ref_type=heads#L22

Steps to reproduce

Set the value for storageClass: '-'

Configuration used

(Please provide a sanitized version of the configuration used wrapped in a code block (```yaml))

gitlab-runner:
  runners:
    privileged: true
global:
  hosts:
    domain: {redacted}
    externalIP: {redacted}
  kas:
    enabled: true
minio:
  replicas: 1
gitlab:
  toolbox:
    backups:
      cron:
        enabled: true
        concurrencyPolicy: Replace
        failedJobsHistoryLimit: 1
        schedule: "10 * * * *"
        successfulJobsHistoryLimit: 3
        suspend: false
        backoffLimit: 6
        safeToEvict: false
        restartPolicy: "OnFailure"
        persistence:
          enabled: true
          accessMode: ReadWriteOnce
          storageClass: '-'
          size: 10Gi

Current behavior

➜  zendesk-tickets kubectl describe pvc -n gl gitlab-toolbox-backup-tmp 
Name:          gitlab-toolbox-backup-tmp
Namespace:     gl
StorageClass:  
Status:        Pending
Volume:        
Labels:        app=toolbox
               app.kubernetes.io/managed-by=Helm
               chart=toolbox-7.10.3
               heritage=Helm
               release=gitlab
Annotations:   meta.helm.sh/release-name: gitlab
               meta.helm.sh/release-namespace: gl
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      
Access Modes:  
VolumeMode:    Filesystem
Used By:       gitlab-toolbox-backup-28633450-tghmq
Events:
  Type    Reason         Age                From                         Message
  ----    ------         ----               ----                         -------
  Normal  FailedBinding  13s (x3 over 30s)  persistentvolume-controller  no persistent volumes available for this claim and no storage class is set

Expected behavior

The volume is able to bind to the default storage class.

➜  zendesk-tickets kubectl get storageclasses.storage.k8s.io 
NAME                     PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
premium-rwo              pd.csi.storage.gke.io   Delete          WaitForFirstConsumer   true                   34d
standard                 kubernetes.io/gce-pd    Delete          Immediate              true                   34d
standard-rwo (default)   pd.csi.storage.gke.io   Delete          WaitForFirstConsumer   true                   34d

Versions

• Chart: (tagged version | branch | hash git rev-parse HEAD)
• Platform:
  • Cloud: GKE
• Kubernetes: (kubectl version)
  • Client:v1.29.2
  • Server:v1.28.9-gke.1000000
• Helm: (helm version)
  • Client: version.BuildInfo{Version:"v3.14.2", GitCommit:"c309b6f0ff63856811846ce18f3bdc93d2b4d54b", GitTreeState:"clean", GoVersion:"go1.22.0"}

Relevant logs

(Please provide any relevate log snippets you have collected, using code blocks (```) to format)