deps: update vstest monorepo to 18.8.0

Author: renovate[bot]

Directory.Packages.props

@@ -2,9 +2,9 @@
   <ItemGroup>
     <PackageVersion Include="Expecto" Version="[10.2.3,)" />
     <PackageVersion Include="FSharp.Core" Version="[7.0.200,)" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.0" />
     <PackageVersion Include="Microsoft.Testing.Extensions.VSTestBridge" Version="2.3.2" />
     <PackageVersion Include="Microsoft.Testing.Platform.MSBuild" Version="2.3.2" />
-    <PackageVersion Include="Microsoft.TestPlatform.ObjectModel" Version="18.7.0" />
+    <PackageVersion Include="Microsoft.TestPlatform.ObjectModel" Version="18.8.0" />
   </ItemGroup>
 </Project>