build(deps): Update dependency Microsoft.CodeAnalysis.CSharp to version 4

Updates-dependency: Microsoft.CodeAnalysis.CSharp
Updates-dependency-from-version: 3.11.0
Updates-dependency-to-version: 4.0.1
Co-authored-by: Renovate Bot <bot@renovateapp.com>
Pull-Request: #174

Author: renovate[bot]

src/MdDocs.TestHelpers/Grynwald.MdDocs.TestHelpers.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.11.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.0.1" />
     <PackageReference Include="Grynwald.Utilities" Version="1.6.11-pre" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="Mono.Cecil" Version="0.11.4" />