docs: Update mixed routing example with improved compatibility for Se…

…rver Actions (#1187)

Passing the request headers as response headers messes with server
actions. vercel/next.js#50659

We need to pass the updated request headers to the NextResponse's
request object.

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Co-authored-by: Jan Amann <jan@amann.work>

examples/example-app-router-mixed-routing/src/middleware.ts

@@ -14,7 +14,7 @@ export default function middleware(request: NextRequest) {
   if (isAppRoute) {
     // Add a hint that we can read in `i18n.ts`
     request.headers.set('x-app-route', 'true');
-    return NextResponse.next({headers: request.headers});
+    return NextResponse.next({request: {headers: request.headers}});
   } else {
     return intlMiddleware(request);
   }