TestTransferLeader in realcluster is flaky

[okJiang]

Flaky Test

Which jobs are failing

TestTransferLeader

CI link

https://do.pingcap.net/jenkins/blue/organizations/jenkins/tikv%2Fpd%2Fpull_integration_realcluster_test/detail/pull_integration_realcluster_test/191/pipeline/

=== RUN   TestTransferLeader
    scheduler_test.go:67: 
        	Error Trace:	/home/jenkins/agent/workspace/tikv/pd/pull_integration_realcluster_test/pd/tests/integrations/realcluster/scheduler_test.go:67
        	Error:      	"[balance-hot-region-scheduler balance-leader-scheduler balance-region-scheduler]" should have 5 item(s), but has 3
        	Test:       	TestTransferLeader
--- FAIL: TestTransferLeader (4.62s)

Reason for failure (if possible)

Anything else