Add explanatory comment for service scope usage

Add comment explaining why service scope is necessary to handle scoped services properly and avoid DI validation issues.

Co-authored-by: davidwengier <[email protected]>

Author: Copilot

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/RazorSourceGeneratorTestsBase.cs

@@ -151,6 +151,8 @@ protected static async Task<string> RenderRazorPageAsync(Compilation compilation
         });
         var app = appBuilder.Build();
 
+        // Create a service scope to properly handle scoped services like IViewBufferScope.
+        // ASP.NET Core's DI validation prevents resolving scoped services from the root provider.
         using var scope = app.Services.CreateScope();
         var httpContext = new DefaultHttpContext
         {