refs and cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -8,8 +8,8 @@
     <PackageVersion Include="Microsoft.CodeAnalysis.Analyzers" Version="3.11.0" Pinned="true" />
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp" Version="4.9.2" Pinned="true" />
     <PackageVersion Include="Microsoft.CodeAnalysis.VisualBasic" Version="4.9.2" Pinned="true" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
-    <PackageVersion Include="Polyfill" Version="9.24.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
+    <PackageVersion Include="Polyfill" Version="10.0.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.172" />
     <PackageVersion Include="Verify" Version="31.15.0" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />