Update lazy loading WASM guidance (#20027)

Author: guardrex

aspnetcore/blazor/webassembly-lazy-load-assemblies.md

@@ -90,7 +90,7 @@ The `LazyAssemblyLoader` provides the `LoadAssembliesAsync` method that:
 The framework's lazy loading implementation supports lazy loading with prerendering in a hosted Blazor solution. During prerendering, all assemblies, including those marked for lazy loading, are assumed to be loaded. Manually register `LazyAssemblyLoader` in the *Server* project's `Startup.ConfigureServices` method (`Startup.cs`):
 
 ```csharp
-services.AddSingleton<LazyAssemblyLoader>();
+services.AddScoped<LazyAssemblyLoader>();
 ```
 
 ### User interaction with `<Navigating>` content