Update dependency Microsoft.NET.Test.Sdk to 18.4.0 (#285)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

Directory.Packages.props

@@ -10,7 +10,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="MessagePack" Version="2.5.198" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
     <PackageVersion Include="Microsoft.VisualStudio.Composition" Version="17.13.41" />
     <PackageVersion Include="Microsoft.VisualStudio.Interop" Version="17.14.40260" />
     <PackageVersion Include="Microsoft.VisualStudio.SDK.Analyzers" Version="17.7.79" />