refs and cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -6,7 +6,7 @@
   <ItemGroup>
     <PackageVersion Include="DocumentFormat.OpenXml" Version="3.1.1" />
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="27.0.2" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageVersion Include="NodaTime" Version="3.2.0" />
     <PackageVersion Include="NUnit" Version="4.2.2" />
     <PackageVersion Include="NUnit3TestAdapter" Version="4.6.0" />