test: add short sleep before channel assert to account for gossip propagation
test: add short sleep before channel assert to account for gossip propagation

This commit adds a short sleep before a channel assertion in the
`testMaxPendingChannels` test. This sleep serves to give the nodes
enough time to propagate the new channel announcement over the
authenticated gossip system. Without this sleep, the call may be issued
in a state wherein only half of the channel announcement has fully
propagated.

AndrewSamokhvalov/lnd,AndrewSamokhvalov/lnd,bryanvu/lnd,ddustin/lnd,bryanvu/lnd,LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd,ddustin/lnd