it's a pretty recent change in MCO:
https://github.com/openshift/machine-config-operator/pull/2686

please reopen a bug there if not removed at the end of OCP upgrade.

@stirabos@redhat.com, currently the cluster is not undergoing any ocp upgrade and the nodes are still tainted:
=================================
[cnv-qe-jenkins@c01-cnv410-upg-6cltm-executor ~]$ kubectl get clusterversion -A
NAME      VERSION                              AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.10.0-0.nightly-2021-12-21-130047   True        False         11h     Cluster version is 4.10.0-0.nightly-2021-12-21-130047
[cnv-qe-jenkins@c01-cnv410-upg-6cltm-executor ~]$ kubectl get node c01-cnv410-upg-6cltm-master-0 -o json | jq ".spec"
{
  "providerID": "openstack:///a098fde7-6bb8-4e78-a778-0579f81c3cec",
  "taints": [
    {
      "effect": "NoSchedule",
      "key": "node-role.kubernetes.io/master"
    },
    {
      "effect": "PreferNoSchedule",
      "key": "UpdateInProgress"
    }
  ]
}
[cnv-qe-jenkins@c01-cnv410-upg-6cltm-executor ~]$

*** This bug has been marked as a duplicate of bug 2035005 ***