test random failed in TestExtractStartTs

[LittleFall]

Bug Report

pr: #24516

ci test name: idc-jenkins-ci-tidb/check_dev_2

logs: https://ci.pingcap.net/blue/rest/organizations/jenkins/pipelines/tidb_ghpr_check_2/runs/3707/log/?start=0

[2021-05-12T09:10:16.971Z] PASS: region_cache_test.go:183: testRegionCacheSuite.TestDropStore	0.000s
[2021-05-12T09:10:16.971Z] [2021/05/12 17:10:10.383 +08:00] [WARN] [client_batch.go:751] ["send request is cancelled"] [to=store1] [cause="context canceled"]
[2021-05-12T09:10:16.971Z] 
[2021-05-12T09:10:16.971Z] ----------------------------------------------------------------------
[2021-05-12T09:10:16.971Z] FAIL: extract_start_ts_test.go:64: extractStartTsSuite.TestExtractStartTs
[2021-05-12T09:10:16.971Z] 
[2021-05-12T09:10:16.971Z] extract_start_ts_test.go:102:
[2021-05-12T09:10:16.971Z]     c.Assert(result, Equals, expected)
[2021-05-12T09:10:16.971Z] ... obtained uint64 = 0x5e57f56c0b40000
[2021-05-12T09:10:16.971Z] ... expected uint64 = 0x5e57f56c0b00000

[ti-srebot]

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