[testnet] use different dns for testnet config

don't confuse with ostn

Signed-off-by: Leo Chen <leo@harmony.one>

internal/configs/sharding/testnet.go

@@ -22,9 +22,9 @@ const (
 	testnetVdfDifficulty = 10000 // This takes about 20s to finish the vdf
 
 	// TestNetHTTPPattern is the http pattern for testnet.
-	TestNetHTTPPattern = "https://api.s%d.os.hmny.io"
+	TestNetHTTPPattern = "https://api.s%d.tn.hmny.io"
 	// TestNetWSPattern is the websocket pattern for testnet.
-	TestNetWSPattern = "wss://ws.s%d.os.hmny.io"
+	TestNetWSPattern = "wss://ws.s%d.tn.hmny.io"
 )
 
 func (testnetSchedule) InstanceForEpoch(epoch *big.Int) Instance {