Leak test testRestoreSchemaSuite.TearDownSuite

[zhouqiang-cl]

Bug Report

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[2021-08-07T21:48:53.751Z] FAIL: db_test.go:49: testRestoreSchemaSuite.TearDownSuite

[2021-08-07T21:48:53.751Z] 

[2021-08-07T21:48:53.751Z] db_test.go:51:

[2021-08-07T21:48:53.751Z]     testleak.AfterTest(c)()

[2021-08-07T21:48:53.751Z] /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/util/testleak/leaktest.go:169:

[2021-08-07T21:48:53.751Z]     c.Errorf("Test %s check-count %d appears to have leaked: %v", c.TestName(), cnt, g)

[2021-08-07T21:48:53.752Z] ... Error: Test  check-count 50 appears to have leaked: github.com/tikv/client-go/v2/tikv.(*KVStore).safeTSUpdater(0xc000b0ad80)

[2021-08-07T21:48:53.752Z] 	/nfs/cache/mod/github.com/tikv/client-go/v2@v2.0.0-alpha.0.20210727120905-55155ad2e543/tikv/kv.go:500 +0x194

[2021-08-07T21:48:53.752Z] created by github.com/tikv/client-go/v2/tikv.NewKVStore

[2021-08-07T21:48:53.752Z] 	/nfs/cache/mod/github.com/tikv/client-go/v2@v2.0.0-alpha.0.20210727120905-55155ad2e543/tikv/kv.go:186 +0x429

1. Minimal reproduce step (Required)

in ci https://ci.pingcap.net/blue/organizations/jenkins/tidb-unit-test-nightly/detail/tidb-unit-test-nightly/7873/pipeline

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

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