Bump Microsoft.Net.Compilers.Toolset from 3.9.0-3.final to 3.9.0 (#96)

Bumps [Microsoft.Net.Compilers.Toolset](https://github.com/dotnet/roslyn) from 3.9.0-3.final to 3.9.0.
- [Release notes](https://github.com/dotnet/roslyn/releases)
- [Changelog](https://github.com/dotnet/roslyn/blob/main/docs/Breaking%20API%20Changes.md)
- [Commits](https://github.com/dotnet/roslyn/commits/v3.9.0)

Signed-off-by: dependabot[bot] <support@github.com>

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

Directory.Build.props

@@ -29,7 +29,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="5.0.3" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="3.9.0-3.final" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="3.9.0" PrivateAssets="all" />
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" PrivateAssets="all" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="all" />
     <PackageReference Include="Nerdbank.GitVersioning" Version="3.3.37" PrivateAssets="all" />