deps: update vstest monorepo to 18.6.0 (#276)

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

Author: renovate[bot]

Directory.Packages.props

@@ -2,9 +2,9 @@
   <ItemGroup>
     <PackageVersion Include="Expecto" Version="[10.2.2, 11.0)" />
     <PackageVersion Include="FSharp.Core" Version="[7.0.200,)" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
     <PackageVersion Include="Microsoft.Testing.Extensions.VSTestBridge" Version="1.9.1" />
     <PackageVersion Include="Microsoft.Testing.Platform.MSBuild" Version="1.9.1" />
-    <PackageVersion Include="Microsoft.TestPlatform.ObjectModel" Version="18.5.1" />
+    <PackageVersion Include="Microsoft.TestPlatform.ObjectModel" Version="18.6.0" />
   </ItemGroup>
 </Project>