metrics: fix typo (#9046)

ref #8678

Signed-off-by: Ryan Leung <rleungx@gmail.com>

Co-authored-by: ti-chi-bot[bot] <108142056+ti-chi-bot[bot]@users.noreply.github.com>

client/metrics/metrics.go

@@ -200,7 +200,7 @@ func initMetrics(constLabels prometheus.Labels) {
 			Name:        "circuit_breaker_count",
 			Help:        "Circuit breaker counters",
 			ConstLabels: constLabels,
-		}, []string{"name", "success"})
+		}, []string{"name", "event"})
 }
 
 // CmdDurationXXX and CmdFailedDurationXXX are the durations of the client commands.