chore(deps): update dependency microsoft.net.test.sdk to v18 (#126)

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

Author: renovate[bot]

src/directory.packages.props

@@ -30,7 +30,7 @@
     <PackageVersion Include="FluentAssertions" Version="8.6.0" />
     <PackageVersion Include="FluentAssertions.Analyzers" Version="0.34.1" />
     <PackageVersion Include="ReactiveUI.Testing" Version="20.4.1" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <PackageVersion Include="Microsoft.Reactive.Testing" Version="6.0.2" />
   </ItemGroup>