[skip e2e]Improve log (#13706)

Signed-off-by: Nsunby <bingyi.sun@zilliz.com>
Co-authored-by: Nsunby <bingyi.sun@zilliz.com>

internal/datacoord/server.go

@@ -454,7 +454,7 @@ func (s *Server) startDataNodeTtLoop(ctx context.Context) {
 			}
 			msgPack := ttMsgStream.Consume()
 			if msgPack == nil {
-				log.Debug("receive nil tt msg, shutdown tt channel")
+				log.Debug("receive nil timetick msg and shutdown timetick channel")
 				return
 			}
 			for _, msg := range msgPack.Msgs {