DATA RACE in the TestTableRestoreSuite

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

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

3. What did you see instead (Required)

==================
WARNING: DATA RACE
Read at 0x00c000b4a508 by goroutine 224:
  github.com/pingcap/tidb/pkg/lightning/backend/tidb.(*tidbEncoder).Encode()
      pkg/lightning/backend/tidb/tidb.go:529 +0xcb
  github.com/pingcap/tidb/lightning/pkg/importer.(*chunkProcessor).encodeLoop()
      lightning/pkg/importer/chunk_process.go:458 +0x29a1
  github.com/pingcap/tidb/lightning/pkg/importer.(*chunkProcessor).process()
      lightning/pkg/importer/chunk_process.go:209 +0xbad
  github.com/pingcap/tidb/lightning/pkg/importer.(*TableImporter).preprocessEngine.func3()
      lightning/pkg/importer/table_import.go:792 +0x2c9
  github.com/pingcap/tidb/lightning/pkg/importer.(*TableImporter).preprocessEngine.func5()
      lightning/pkg/importer/table_import.go:824 +0x4f
Previous write at 0x00c000b4a508 by goroutine 221:
  github.com/pingcap/tidb/pkg/lightning/backend/tidb.(*tidbEncoder).Encode()
      pkg/lightning/backend/tidb/tidb.go:543 +0x1178
  github.com/pingcap/tidb/lightning/pkg/importer.(*chunkProcessor).encodeLoop()
      lightning/pkg/importer/chunk_process.go:458 +0x29a1
  github.com/pingcap/tidb/lightning/pkg/importer.(*chunkProcessor).process()
      lightning/pkg/importer/chunk_process.go:209 +0xbad
  github.com/pingcap/tidb/lightning/pkg/importer.(*TableImporter).preprocessEngine.func3()
      lightning/pkg/importer/table_import.go:792 +0x2c9
  github.com/pingcap/tidb/lightning/pkg/importer.(*TableImporter).preprocessEngine.func5()
      lightning/pkg/importer/table_import.go:824 +0x4f
Goroutine 224 (running) created at:
  github.com/pingcap/tidb/lightning/pkg/importer.(*TableImporter).preprocessEngine()
      lightning/pkg/importer/table_import.go:782 +0x1f8d
  github.com/pingcap/tidb/lightning/pkg/importer.(*tableRestoreSuite).TestRestoreEngineFailed()
      lightning/pkg/importer/table_import_test.go:452 +0x25e4
  runtime.call16()
      src/runtime/asm_amd64.s:747 +0x42
  reflect.Value.Call()
      GOROOT/src/reflect/value.go:380 +0xb5
  github.com/stretchr/testify/suite.Run.func1()
      external/com_github_stretchr_testify/suite/suite.go:202 +0x766
  testing.tRunner()
      GOROOT/src/testing/testing.go:1595 +0x261
  testing.(*T).Run.func1()
      GOROOT/src/testing/testing.go:1648 +0x44
Goroutine 221 (finished) created at:
  github.com/pingcap/tidb/lightning/pkg/importer.(*TableImporter).preprocessEngine()
      lightning/pkg/importer/table_import.go:782 +0x1f8d
  github.com/pingcap/tidb/lightning/pkg/importer.(*tableRestoreSuite).TestRestoreEngineFailed()
      lightning/pkg/importer/table_import_test.go:452 +0x25e4
  runtime.call16()
      src/runtime/asm_amd64.s:747 +0x42
  reflect.Value.Call()
      GOROOT/src/reflect/value.go:380 +0xb5
  github.com/stretchr/testify/suite.Run.func1()
      external/com_github_stretchr_testify/suite/suite.go:202 +0x766
  testing.tRunner()
      GOROOT/src/testing/testing.go:1595 +0x261
  testing.(*T).Run.func1()
      GOROOT/src/testing/testing.go:1648 +0x44
================== 

4. What is your TiDB version? (Required)

[lance6716]

/assign @lyzx2001