[release-1.6] cluster-machines-ready breaks when running on a sylva 1.7 mgmt cluster

The current code in cluster-machines-ready of release-1.6 breaks when running on a mgmt cluster in version 1.7:

error: timed out waiting for the condition on rke2controlplanes/swct-zioc-team--zioc-control-plane

This is because the status field changed between v1beta1 and v1beta2 of the RKE2Controlplane resource.

There are possibly other similar adjustments that are required for other CRDs.

We can probably leverage apiVersion in kubectl calls to benefit from api versioning and translation webhooks, but in the rke2controlplane case this won't be sufficient.

/cc @feleouet (who noticed this first)