GCP volumes and claims can have mismatched provisioner

[afharvey]

Describe the bug
A panic occurs because of a nil pointer in processPersistentVolumeClaim.
This is because the provisioner on a claim can be different to the provisioner on a volume.
I've found this on a GKE cluster where the volume was "migrated" from GCE to CSI.

To Reproduce
Steps to reproduce the behavior:

1. Create a PersistentVolumeClaim on GKE using your clusters "default" provisioner
2. A PersistentVolume is provisioned by GCE
3. The PersistentVolume is migrated to CSI
4. The PersistentVolumeClaim is provisioned by CSI
5. processPersistentVolumeClaim panics because it looks for the volumeID on a nil field

Expected behavior
Finds the volumeID on the PersistentVolume regardless of provisioner on PersistentVolumeClaim.

Additional context
I think this could fix the issue: https://github.com/afharvey/k8s-pvc-tagger/pull/1/files
I tried to keep the changes limited to GCP.
I'm happy to try and fix this or take another approach.
I've only seen this on GCP. Azure and AWS work great.

Here are the K8s resources which cause the panic (and crash looping).

PersistentVolumeClaim - GCP_PD_CSI provisioner

volume.kubernetes.io/storage-provisioner: pd.csi.storage.gke.io

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  annotations:
    k8s-pvc-tagger/ignore: "true"
    pv.kubernetes.io/bind-completed: "yes"
    pv.kubernetes.io/bound-by-controller: "yes"
    volume.beta.kubernetes.io/storage-provisioner: pd.csi.storage.gke.io
    volume.kubernetes.io/storage-provisioner: pd.csi.storage.gke.io
  creationTimestamp: "2025-03-04T13:54:47Z"
  finalizers:
  - kubernetes.io/pvc-protection
  labels:
    component: my-component
  name: my-component
  namespace: default
  resourceVersion: "809902313"
  uid: 7490859c-9e2f-4c71-b157-8d42205e4325
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 500Mi
  storageClassName: standard
  volumeMode: Filesystem
  volumeName: pvc-7490859c-9e2f-4c71-b157-8d42205e4325
status:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 1Gi
  phase: Bound

PersistentVolume - GCP_PD_LEGACY provisioner

pv.kubernetes.io/migrated-to: pd.csi.storage.gke.io
pv.kubernetes.io/provisioned-by: kubernetes.io/gce-pd

apiVersion: v1
kind: PersistentVolume
metadata:
  annotations:
    pv.kubernetes.io/migrated-to: pd.csi.storage.gke.io
    pv.kubernetes.io/provisioned-by: kubernetes.io/gce-pd
    volume.kubernetes.io/provisioner-deletion-secret-name: ""
    volume.kubernetes.io/provisioner-deletion-secret-namespace: ""
  creationTimestamp: "2025-03-04T13:54:51Z"
  finalizers:
  - kubernetes.io/pv-protection
  - external-attacher/pd-csi-storage-gke-io
  labels:
    topology.kubernetes.io/region: europe-west2
    topology.kubernetes.io/zone: europe-west2-c
  name: pvc-7490859c-9e2f-4c71-b157-8d42205e4325
  resourceVersion: "807636430"
  uid: e709c9c4-abc7-4529-9207-c52faef0c966
spec:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 1Gi
  claimRef:
    apiVersion: v1
    kind: PersistentVolumeClaim
    name: my-component
    namespace: default
    resourceVersion: "807636314"
    uid: 7490859c-9e2f-4c71-b157-8d42205e4325
  gcePersistentDisk:
    fsType: ext4
    pdName: pvc-7490859c-9e2f-4c71-b157-8d42205e4325
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: topology.kubernetes.io/zone
          operator: In
          values:
          - europe-west2-c
        - key: topology.kubernetes.io/region
          operator: In
          values:
          - europe-west2
  persistentVolumeReclaimPolicy: Delete
  storageClassName: standard
  volumeMode: Filesystem
status:
  lastPhaseTransitionTime: "2025-03-04T13:54:51Z"
  phase: Bound