Erroneous "Failed to publish Block" error message when MEV sends block before us

[Menduist]

When the MEV producer sends the block fast enough on the GossipSub network, it can reach us before we had time to publish it

In that case, logs will show:

Block not sent [..]  error="No peers on libp2p topic"

even though the block already went through the network

This is because libp2p doesn't expose the failure type of publish, it just says that it failed.

Requires: vacp2p/nim-libp2p#950