Keep alive ticker is wrongly stopped

[rleungx]

Bug Report

related to https://github.com/tidbcloud/pd-cse/issues/153.

pd/pkg/mcs/discovery/register.go

Lines 84 to 107 in 0c537bb

	t := time.NewTicker(time.Duration(sr.ttl) * time.Second / 2)
	for {
	select {
	case <-sr.ctx.Done():
	log.Info("exit register process", zap.String("key", sr.key))
	t.Stop()
	return
	default:
	}
	<-t.C
	resp, err := sr.cli.Grant(sr.ctx, sr.ttl)
	if err != nil {
	log.Error("grant lease failed", zap.String("key", sr.key), zap.Error(err))
	t.Stop()
	continue
	}
	if _, err := sr.cli.Put(sr.ctx, sr.key, sr.value, clientv3.WithLease(resp.ID)); err != nil {
	log.Error("put the key failed", zap.String("key", sr.key), zap.Error(err))
	t.Stop()
	continue
	}
	}

Line 98 and line 104 are wrongly stopped by #6720.

What version of PD are you using (pd-server -V)?

cse only