Fix DI scoping issue in RazorSourceGeneratorTestsBase

- Create scoped service provider instead of using root provider
- Update both RequestServices and ActivatorUtilities.CreateInstance to use scoped provider
- Properly dispose scope with using statement

This fixes test failures in environments with stricter DI validation and aligns with ASP.NET Core best practices.

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

Author: Copilot

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

@@ -150,9 +150,11 @@ protected static async Task<string> RenderRazorPageAsync(Compilation compilation
             }
         });
         var app = appBuilder.Build();
+        
+        using var scope = app.Services.CreateScope();
         var httpContext = new DefaultHttpContext
         {
-            RequestServices = app.Services
+            RequestServices = scope.ServiceProvider
         };
         var requestFeature = new HttpRequestFeature
         {
@@ -184,7 +186,7 @@ protected static async Task<string> RenderRazorPageAsync(Compilation compilation
             .ToImmutableArray();
 
         // Render the page.
-        var view = ActivatorUtilities.CreateInstance<RazorView>(app.Services,
+        var view = ActivatorUtilities.CreateInstance<RazorView>(scope.ServiceProvider,
             /* IReadOnlyList<IRazorPage> viewStartPages */ viewStarts,
             /* IRazorPage razorPage */ page);
         await view.RenderAsync(viewContext);