tidb: unit test TestSyncerSimple fails

FAIL:TestSyncerSimple

Bug Report

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1. What did you do? If possible, provide a recipe for reproducing the error.

https://internal.pingcap.net/idc-jenkins/blue/organizations/jenkins/tidb_ghpr_check_2/detail/tidb_ghpr_check_2/23932/pipeline/

https://internal.pingcap.net/idc-jenkins/blue/organizations/jenkins/tidb_ghpr_unit_test/detail/tidb_ghpr_unit_test/23968/pipeline/

[2020-02-13T04:01:46.004Z] --- FAIL: TestSyncerSimple (12.90s)

[2020-02-13T04:01:46.004Z]     syncer_test.go:119: get udpate version failed

[2020-02-13T04:01:46.004Z] FAIL

1. What did you expect to see?

2. What did you see instead?

3. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?