Update csi-attacher to v.1.2.1 for fix to not ignore ControllerUnpublishErrors

Author: davidz627

deploy/kubernetes/overlays/stable/kustomization.yaml

@@ -13,7 +13,7 @@ images:
   newTag: "v1.2.1-gke.0"
 - name: gke.gcr.io/csi-attacher
   newName: gke.gcr.io/csi-attacher
-  newTag: "v1.2.0-gke.0"
+  newTag: "v1.2.1-gke.0"
 - name: gke.gcr.io/csi-node-driver-registrar
   newName: gke.gcr.io/csi-node-driver-registrar
   newTag: "v1.1.0-gke.0"