chore: Correct o11y available-since date in docs (#14321)

I absolutely knew we were going to miss one of these... just wasn't sure where 😆

Author: elliott-with-the-longest-name-on-github

documentation/docs/30-advanced/68-observability.md

@@ -3,7 +3,7 @@ title: Observability
 ---
 
 <blockquote class="since note">
-	<p>Available since 2.29</p>
+	<p>Available since 2.31</p>
 </blockquote>
 
 Sometimes, you may need to observe how your application is behaving in order to improve performance or find the root cause of a pesky bug. To help with this, SvelteKit can emit server-side [OpenTelemetry](https://opentelemetry.io) spans for the following: