chore(deps): update vstest monorepo to 18.6.0 (#485)

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

Author: renovate[bot]

test/Serilog.Sinks.HttpTests/Serilog.Sinks.HttpTests.csproj

@@ -18,7 +18,7 @@
     </PackageReference>
     <PackageReference Include="Markdig" Version="1.2.0" />
     <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="10.0.8" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
     <PackageReference Include="Serilog.Sinks.File" Version="7.0.0" />
     <PackageReference Include="Serilog.Settings.Configuration" Version="10.0.0" />
     <PackageReference Include="Shouldly" Version="4.3.0" />