metrics: add missing calls to Ticker.Stop in tests (ethereum#20866)

Author: ucwong

metrics/meter_test.go

@@ -26,6 +26,7 @@ func TestMeterDecay(t *testing.T) {
 		ticker: time.NewTicker(time.Millisecond),
 		meters: make(map[*StandardMeter]struct{}),
 	}
+	defer ma.ticker.Stop()
 	m := newStandardMeter()
 	ma.meters[m] = struct{}{}
 	go ma.tick()

metrics/sample_test.go

@@ -346,6 +346,7 @@ func TestUniformSampleConcurrentUpdateCount(t *testing.T) {
 	quit := make(chan struct{})
 	go func() {
 		t := time.NewTicker(10 * time.Millisecond)
+		defer t.Stop()
 		for {
 			select {
 			case <-t.C: