fix(docs-infra): raise SSR fetch limit so the menubar guide prerenders

The aria menubar guide content is 2.9 MB, over the 2 MiB
maxResponseBodySize set in #69379. The fetch fails during prerender,
the navigation error handler redirects to /404, and the prerendered
page is saved as that redirect. Opening /guide/aria/menubar directly
or refreshing it lands on the 404 page.

Raise the limit to 4 MiB. The combobox guide was also within 27 KB of
the old limit.

adev/src/app/app.config.server.ts

@@ -13,7 +13,7 @@ import {appConfig} from './app.config';
 const serverConfig: ApplicationConfig = {
   providers: [
     provideServerRendering(
-      {maxResponseBodySize: 2 * 1024 * 1024},
+      {maxResponseBodySize: 4 * 1024 * 1024},
       withRoutes([{path: '**', renderMode: RenderMode.Prerender}]),
     ),
   ],