Ignition fails adding new nodes to UPI cluster after upgrading to OCP 4.6+

Issue

• Adding new nodes to an OpenShift cluster that has been upgraded to 4.6 fails with the follow ignition error:

  Ignition has failed. Please ensure your config is valid. Note that only
  Ignition spec v3.0.0+ configs are accepted.
  
  A CLI validation tool to check this called ignition-validate can be
  downloaded from GitHub:
    https://github.com/coreos/ignition/releases
  

  Displaying logs from failed units: ignition-fetch-offline.service
  -- Logs begin at Thu 2020-12-10 20:52:42 UTC, end at Thu 2020-12-10 20:52:45 UTC. --
  Dec 10 20:52:44 ignition[649]: no config URL provided
  Dec 10 20:52:44 ignition[649]: reading system config file "/usr/lib/ignition/user.ign"
  Dec 10 20:52:44 systemd[1]: ignition-fetch-offline.service: Main process exited, code=exited, status=1/FAILURE
  Dec 10 20:52:44 ignition[649]: parsing config with SHA512: 85f42e0875f36f9c73b858ecfdaa21fe33df0b6141c302c2b6a17d8fc322346d98cabff5f2b902e92c92325d27b51cb086df6f59e283f0586cccad313df08326
  Dec 10 20:52:44 systemd[1]: ignition-fetch-offline.service: Failed with result 'exit-code'.
  Dec 10 20:52:44 ignition[649]: failed to fetch config: unsupported config version
  Dec 10 20:52:44 systemd[1]: Failed to start Ignition (fetch-offline).
  Dec 10 20:52:44 ignition[649]: failed to acquire config: unsupported config version
  Dec 10 20:52:44 ignition[649]: Ignition failed: unsupported config version