Problem when RP is not register and using -WhatIf parameter

**Describe the bug**
When you run deployment with -WhatIf parameter set to false or true on a new subscription where the resource provider for the deployed resources is not registered the command will fail with:
The subscription must be registered to use namespace 'Microsoft.ManagedServices'.
The whole error is:

```
Error:
DeploymentWhatIfResourceError - Long running operation failed with status 'Failed'. Additional Info:'The request to predict template deployment changes to subscription '' has failed due to a resource error. See details for more information.'
MissingSubscriptionRegistration - The managed services resource provider not allowed to access the subscription ''. The subscription must be registered to use namespace 'Microsoft.ManagedServices'. Please see https://aka.ms/rp-not-register-error for details on how to register subscriptions.
AuthorizationFailed - The client '' with object id '' does not have authorization to perform action 'Microsoft.Resources/subscriptions/read' over scope '/subscriptions/' or the scope is invalid. If access was recently granted, please refresh your credentials.

```

This works perfectly fine if the -WhatIf parameter is completely missing.
For authentication I am using access token which is generated by refresh token. The refresh token is generated by Azure AD app registration that impersonates user that has Admin Agent (AOBO) (CSP scenario). New-AzSubscriptionDeployment should work the same way no matter if you are using -WhatIf parameter or not.

**Client** [e.g. PowerShell, CLI, API)
Powershell

Reproduce New-AzSubscriptionDeployment on a new subscription with -WhatIf set to true and false, using the described access-token authentication, then compare it with a deployment that omits -WhatIf. Investigate the reported Microsoft.ManagedServices registration, subscription-read authorization, and DeploymentWhatIfResourceError details; done when WhatIf and normal deployment behave consistently for the same credentials.

Written by the indexing model from the issue text.