Fix build breaks

Author: AArnott

Directory.Packages.props

@@ -19,6 +19,7 @@
     <PackageVersion Include="Microsoft.CodeAnalysis.VisualBasic.CodeFix.Testing.XUnit" Version="$(CodefixTestingVersion)" />
     <PackageVersion Include="Microsoft.CodeAnalysis.VisualBasic.Workspaces" version="$(CodeAnalysisVersion)" />
     <PackageVersion Include="Microsoft.CodeAnalysis" Version="$(CodeAnalysisVersion)" />
+    <PackageVersion Include="Microsoft.CSharp" Version="4.7.0" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.6.2" />
     <PackageVersion Include="Microsoft.VisualStudio.Internal.MicroBuild.NonShipping" Version="$(MicroBuildVersion)" />
     <PackageVersion Include="Microsoft.VisualStudio.Threading.Analyzers" Version="17.7.28" />

test/Microsoft.VisualStudio.Composition.Tests/Microsoft.VisualStudio.Composition.Tests.csproj

@@ -6,6 +6,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="DiffPlex" />
+    <PackageReference Include="Microsoft.CSharp" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="Nullable" PrivateAssets="all" />
     <PackageReference Include="xunit.extensibility.execution" />