Remove-EntraServicePrincipalKeyCredential calls the removeKey method which requires a Proof...
https://learn.microsoft.com/en-us/graph/api/serviceprincipal-removekey?view=graph-rest-1.0&tabs=http
However this cmdlet does not allow to pass Proof which results in a 403
Remove-EntraServicePrincipalKeyCredential needs to support passing Proof property