Re-enqueue message when outbound stream fails

An outbound stream carries the first message for the remote node when upgrading in the
`OutboundOpenInfo`. Thus far the GossipSub handler would drop the message when the outbound stream
fails to upgrade.

This could e.g. lead to a remote peer receiving a GRAFT without a previous SUBSCRIBE.

With this commit the message carried in the upgrade's `OutboundOpenInfo` is re-enqueued.

protocols/gossipsub/src/handler.rs

@@ -531,9 +531,12 @@ impl ConnectionHandler for Handler {
             }
             ConnectionEvent::DialUpgradeError(DialUpgradeError {
                 error: ConnectionHandlerUpgrErr::Timeout | ConnectionHandlerUpgrErr::Timer,
-                ..
+                info,
             }) => {
                 log::debug!("Dial upgrade error: Protocol negotiation timeout.");
+
+                // Re-enqueue message.
+                self.send_queue.insert(0, info);
             }
             ConnectionEvent::DialUpgradeError(DialUpgradeError {
                 error: ConnectionHandlerUpgrErr::Upgrade(UpgradeError::Apply(e)),