differingProperties always propagated on adapter resource

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest version
• Search the existing issues.

Summary

When writing the docs for #848, I noticed that the differingProperties are always being propagated. For example, executing the following:

$instance = @{
    Name        = 'Spooler'
    StartupType = 'Automatic'
} | ConvertTo-Json

dsc resource test --resource PSDesiredStateConfiguration/Service --input $instance

Returns the desiredState equals true. I would expect the differingProperties to be empty. Instead, both Name and StartupType are returned.

Steps to reproduce

See description

Expected behavior

Return `differingProperties: []`

Actual behavior

Returns both properties

Error details

Environment data

Name                           Value
----                           -----
PSVersion                      5.1.19041.5848
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.19041.5848
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

Version

dsc 3.1.0-preview.6

Visuals

No response

Start by reproducing the dsc resource test command with the PSDesiredStateConfiguration/Service adapter resource and inspect how differingProperties is produced. Done means matching properties no longer appear in that list and a regression test covers the reported input.