Bump Microsoft.Net.Compilers.Toolset from 4.1.0 to 4.2.0 (#7224)

Bumps [Microsoft.Net.Compilers.Toolset](https://github.com/dotnet/roslyn) from 4.1.0 to 4.2.0.
- [Release notes](https://github.com/dotnet/roslyn/releases)
- [Changelog](https://github.com/dotnet/roslyn/blob/main/docs/Breaking%20API%20Changes.md)
- [Commits](dotnet/roslyn@v4.1.0...Visual-Studio-2019-Version-16.0-Preview-4.2)

---
updated-dependencies:
- dependency-name: Microsoft.Net.Compilers.Toolset
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Directory.Build.props

@@ -99,6 +99,6 @@
   <Import Condition="'$(EnvironmentBuildPropsImported)' != 'True'" Project="$(MSBuildThisFileDirectory)eng\Environment.Build.props" />
   <Import Condition="'$(SampleProject)' != 'True' and '$(CI)' == 'true'" Project="$(MSBuildThisFileDirectory)eng\SourceLink.Build.props" />
   <ItemGroup Condition="'$(MSBuildVersion)' != '' AND '$(MSBuildVersion)' &lt; '16.7.0'  ">
-    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="4.1.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="4.2.0" PrivateAssets="all" />
   </ItemGroup>
 </Project>