Update dependency Verify.NUnit to 28.15.0

Author: renovate-bot

src/Directory.Packages.props

@@ -20,6 +20,6 @@
     <PackageVersion Include="System.Linq.Async" Version="6.0.1" />
     <PackageVersion Include="System.Text.Json" Version="9.0.3" />
     <PackageVersion Include="Verify.Http" Version="6.4.1" />
-    <PackageVersion Include="Verify.NUnit" Version="28.13.0" />
+    <PackageVersion Include="Verify.NUnit" Version="28.15.0" />
   </ItemGroup>
 </Project>