fix: rendezvous identify example

This pr closes libp2p#5388 by explicitly adding the local observed address, noting this is out of protocol behaviour in non-example cases

Pull-Request: libp2p#5496.

examples/rendezvous/src/bin/rzv-identify.rs

@@ -76,8 +76,12 @@ async fn main() {
             }
             // once `/identify` did its job, we know our external address and can register
             SwarmEvent::Behaviour(MyBehaviourEvent::Identify(identify::Event::Received {
+                info,
                 ..
             })) => {
+                // Register our external address. Needs to be done explicitly
+                // for this case, as it's a local address.
+                swarm.add_external_address(info.observed_addr);
                 if let Err(error) = swarm.behaviour_mut().rendezvous.register(
                     rendezvous::Namespace::from_static("rendezvous"),
                     rendezvous_point,