refs and cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -5,7 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.2" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.161" />
     <PackageVersion Include="Paramore.Brighter" Version="9.9.12" />
     <PackageVersion Include="Verify" Version="30.19.2" />