update libp2p to 0.55 (#6889)

Updates libp2p to `0.55`.
Will address the deprecations in a subsequent PR

beacon_node/lighthouse_network/src/discovery/mod.rs

@@ -994,7 +994,7 @@ impl<E: EthSpec> NetworkBehaviour for Discovery<E> {
         &mut self,
         _peer_id: PeerId,
         _connection_id: ConnectionId,
-        _event: void::Void,
+        _event: std::convert::Infallible,
     ) {
     }