capm3/maxSurge 0: MachineDeployments are downscaled during control-plane upgrade

With maxSurge zero, during a Kubernetes upgrade, all MDs will be downscaled by one for a time longer than desirable (during the time needed to roll'update all the CP nodes), while ideally the MDs could remain untouched during the CP nodes rolling update.

Details in this upstream issue: https://github.com/kubernetes-sigs/cluster-api/issues/12187