refs and cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -14,7 +14,7 @@
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.2" />
     <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="9.0.9" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="9.0.9" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <PackageVersion Include="Microsoft.Sbom.Targets" Version="4.1.2" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.161" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />