refs or cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -8,9 +8,9 @@
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageVersion Include="NUnit" Version="4.3.0" />
     <PackageVersion Include="NUnit3TestAdapter" Version="4.6.0" />
-    <PackageVersion Include="Polyfill" Version="7.7.1" />
+    <PackageVersion Include="Polyfill" Version="7.8.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.147" />
-    <PackageVersion Include="System.Collections.Immutable" Version="8.0.0" />
+    <PackageVersion Include="System.Collections.Immutable" Version="9.0.0" />
     <PackageVersion Include="System.Memory" Version="4.6.0" />
   </ItemGroup>
 </Project>