lntest: decrease broadcast timeout for neutrino-backed integration tests

Since we don't have to worry about network latency within our
integration tests, we can shorten the broadcast timeout for neutrino
integration tests from 5s to 1s.

lntest/neutrino.go

@@ -27,6 +27,7 @@ func (b NeutrinoBackendConfig) GenArgs() []string {
 	// We enable validating channels so that we can obtain the outpoint for
 	// channels within the graph and make certain assertions based on them.
 	args = append(args, "--neutrino.validatechannels")
+	args = append(args, "--neutrino.broadcasttimeout=1s")
 	return args
 }