chore(deps): update dependency microsoft.net.test.sdk to v18

Author: lucca-renovate[bot]

Directory.Packages.props

@@ -16,7 +16,7 @@
     <PackageVersion Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.16.0" />
     <PackageVersion Include="System.Diagnostics.PerformanceCounter" Version="9.0.18" />
     <PackageVersion Include="System.IO.Pipelines" Version="9.0.18" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
     <PackageVersion Include="coverlet.msbuild" Version="6.0.4">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>