fix: Cloudflare Containers Stateless Instances getRandom needs await (#24194)

Author: rwv

src/content/docs/containers/examples/stateless.mdx

@@ -23,7 +23,7 @@ class Backend extends Container {
 export default {
 	async fetch(request: Request, env: Env): Promise<Response> {
 		// note: "getRandom" to be replaced with latency-aware routing in the near future
-		const containerInstance = getRandom(env.BACKEND, INSTANCE_COUNT);
+		const containerInstance = await getRandom(env.BACKEND, INSTANCE_COUNT);
 		return containerInstance.fetch(request);
 	},
 };