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

Author: renovate[bot]

test/PortableText.Tests/PortableText.Tests.csproj

@@ -11,7 +11,7 @@
   <ItemGroup>
     <PackageReference Include="AngleSharp" Version="1.0.4" />
     <PackageReference Include="FluentAssertions" Version="6.11.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.3" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
     <PackageReference Include="System.Text.Json" Version="7.0.3" />
     <PackageReference Include="xunit" Version="2.5.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.0">