Failed spot VM machinesets in non-zonal Azure regions

New spot VMs fail to be created by machinesets defining providerSpec.value.spotVMOptions in Azure regions without Availability Zones.

Azure-controller logs the error: Azure Spot Virtual Machine is not supported in Availability Set.

A new availabilitySet is created for each machineset in non-zonal regions, but this only works with normal nodes. Spot VMs and availabilitySets are incompatible as per Microsoft docs for this error: You need to choose to either use an Azure Spot Virtual Machine or use a VM in an availability set, you can't choose both.
From: https://learn.microsoft.com/en-us/azure/virtual-machines/error-codes-spot

    n/a

    Always

1. Follow the instructions to create a machineset to provision spot VMs: 
  https://docs.openshift.com/container-platform/4.12/machine_management/creating_machinesets/creating-machineset-azure.html#machineset-creating-non-guaranteed-instance_creating-machineset-azure

2. New machines will be in Failed state:
$ oc get machines -A
NAMESPACE               NAME                                            PHASE     TYPE              REGION       ZONE   AGE
openshift-machine-api   mabad-test-l5x58-worker-southindia-spot-c4qr5   Failed                                          7m17s
openshift-machine-api   mabad-test-l5x58-worker-southindia-spot-dtzsn   Failed                                          7m17s
openshift-machine-api   mabad-test-l5x58-worker-southindia-spot-tzrhw   Failed                                          7m28s


3. Events in the failed machines show errors creating spot VMs with availabilitySets:
Events:
  Type     Reason             Age                 From                           Message
  ----     ------             ----                ----                           -------
  Warning  FailedCreate       28s                 azure-controller               InvalidConfiguration: failed to reconcile machine "mabad-test-l5x58-worker-southindia-spot-dx78z": failed to create vm mabad-test-l5x58-worker-southindia-spot-dx78z: failure sending request for machine mabad-test-l5x58-worker-southindia-spot-dx78z: cannot create vm: compute.VirtualMachinesClient#CreateOrUpdate: Failure sending request: StatusCode=0 -- Original Error: autorest/azure: Service returned an error. Status=<nil> Code="OperationNotAllowed" Message="Azure Spot Virtual Machine is not supported in Availability Set. For more information, see http://aka.ms/AzureSpot/errormessages."    

     Machines stay in Failed state and nodes are not created

     Machines get created and new spot VM nodes added to the cluster.

    This problem was identified from a customer alert in an ARO cluster. ICM for ref (requires b- MSFT account): https://portal.microsofticm.com/imp/v3/incidents/incident/455463992/summary