azurerm_machine_learning_workspace: fix acctests (#7635)

The machine learning service has changed the delete from a sync operation to an async operation.

Depends on the SDK v44.0.0 PR #7616

azurerm/internal/services/machinelearning/machine_learning_workspace_resource.go

@@ -327,10 +327,15 @@ func resourceArmMachineLearningWorkspaceDelete(d *schema.ResourceData, meta inte
 		return fmt.Errorf("Error parsing Machine Learning Workspace ID `%q`: %+v", d.Id(), err)
 	}
 
-	if _, err := client.Delete(ctx, id.ResourceGroup, id.Name); err != nil {
+	future, err := client.Delete(ctx, id.ResourceGroup, id.Name)
+	if err != nil {
 		return fmt.Errorf("Error deleting Machine Learning Workspace %q (Resource Group %q): %+v", id.Name, id.ResourceGroup, err)
 	}
 
+	if err := future.WaitForCompletionRef(ctx, client.Client); err != nil {
+		return fmt.Errorf("Error waiting for deletion of Machine Learning Workspace %q (Resource Group %q): %+v", id.Name, id.ResourceGroup, err)
+	}
+
 	return nil
 }