[BUG] VirtualMachineResource UpdateAsync with WaitUntil.Completed is not waiting on long running operation to complete

[a-santamaria]

Library name and version

Azure.ResourceManager.Compute 1.6.0.0

Describe the bug

Calling UpdateAsync with WaitUntil.Completed is not waiting on long running operation to complete. We see that the operation returns right away

Expected behavior

method call should only return after the vmss LRO has finished.

Actual behavior

method return right away as soon as the operation is accepted but doesn't wait for the LOR to finish

Reproduction Steps

call UpdateAsync with WaitUntil.Completed. We've seen it in scale operations.

you can see our implementation here: https://msazure.visualstudio.com/One/_git/winfab-RP?path=/src/sfmc/SfmcBackendService/Common/AzureClient/SfmcArmClient.cs&version=GBdevelop&_a=contents

            ```

ArmOperation lro = await virtualMachineScaleSet.UpdateAsync(WaitUntil.Completed, vmssUpdate, cancellationToken);
return lro.Value;

### Environment

_No response_

[jsquire]

@a-santamaria: Please do not assign labels when opening issues in this repository unless assigning it to yourself or team. It interferes with our automation and breaks triage.

[ArthurMa1978]

Same issue as #48740

[ArthurMa1978]

This is a known issue on the service side, the reason is:
The VMSS PATCH LRO returns 200 instead of arm regulation 202.
The response header contains Azure-AsyncOperation which seems like the service want us to poll next link.
But our .NET SDK will ignore the header if the method is patch and status code is 200 at this method. And call the final GET resource operation, end the LRO instantly.
And also, at this point, even with the portal shows the patch still in progress, the get operation returned "provisioningState": "Succeeded".

Here is an issue created to track this on service side.