refs and cleanup

src/Directory.Packages.props

@@ -7,7 +7,7 @@
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="27.0.2" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageVersion Include="NSubstitute" Version="5.1.0" />
-    <PackageVersion Include="Polyfill" Version="5.6.0" />
+    <PackageVersion Include="Polyfill" Version="6.0.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.131" />
     <PackageVersion Include="Verify" Version="25.3.2" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.0" />