chains: switch to new DNS seed for bitcoin testnet

In this commit we switch over to the new DNS seed for Bitcoin’s
testnet. This seed will only serve active nodes that are found on
Bitcoin’s testnet.

chainregistry.go

@@ -605,9 +605,9 @@ var (
 	// TODO(roasbeef): extend and collapse these and chainparams.go into
 	// struct like chaincfg.Params
 	chainDNSSeeds = map[chainhash.Hash][][2]string{
-		bitcoinGenesis: {
+		bitcoinTestnetGenesis: {
 			{
-				"nodes.lightning.directory",
+				"test.nodes.lightning.directory",
 				"soa.nodes.lightning.directory",
 			},
 		},