Describe the bug

Unable to connect or deploy to Hololens using the Build Window / Deploy Options tag. This works fine in 2.7.2.

To reproduce

1. Setup empty MRTK project with the MRTK Tools
2. Load Build Window
3. Fill in Hololens details (username / password)
4. Click Test Connection

Expected behavior

Connection success console message

My setup

• Unity 2020.3.18f1
• MRTK v2.7.3
• HoloLens 2

Additional context

I tracked the issue down to the changes introduced in this merge.
#10033

This await never returns
https://github.com/microsoft/MixedRealityToolkit-Unity/blob/main/Assets/MRTK/Core/Utilities/WebRequestRest/Response.cs#L35

I can get the connection to work by replacing:
https://github.com/microsoft/MixedRealityToolkit-Unity/blob/main/Assets/MRTK/Core/Utilities/WindowsDevicePortal/DevicePortal.cs#L909

return new Response(true, new Task<string>(() => webRequest.GetResponseHeader("Set-Cookie")), () => webRequest.downloadHandler?.data, responseCode);

With:
return new Response(true, webRequest.GetResponseHeader("Set-Cookie"), webRequest.downloadHandler?.data, responseCode);