chore(function): fix code snippet at set-up-function page (#8046)

* Add `.authorization(allow => [allow.guest()])`

Author: tttol

src/pages/[platform]/build-a-backend/functions/set-up-function/index.mdx

@@ -92,6 +92,7 @@ const schema = a.schema({
       name: a.string(),
     })
     .returns(a.string())
+    .authorization(allow => [allow.guest()])
     .handler(a.handler.function(sayHello)),
   // highlight-end
 })