operator: fix nodes informer
operator: fix nodes informer

Commit 6d44f4cd replaced the informer feeding nodes to kvstore
from using corev1.Nodes to CiliumNodes, but the object type
passed to informer isn't updated accordingly, which prevents the
controller from collecting nodes:
```
cilium-operator level=error msg=k8sError error="github.com/cilium/cilium/operator/k8s_node.go:96: expected type *v1.Node, but watch event object had type *v2.CiliumNode" subsys=k8s
```

Note for the longer term: the operator already has a
v2.CiliumNode informer (in operator/cilium_node.go),
maybe k8s_node should use that too.

Signed-off-by: Benjamin Pineau <cf5203523f4517691910cffec2801b9b3ffdb8e8@datadoghq.com>

cilium/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,cilium-team/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,cilium-team/cilium