br: Remove statement from closure to prevent concurrent operation during backup system table (#29730)

[ti-srebot]

cherry-pick #29730 to release-5.3
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/29774

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git push git@github.com:ti-srebot/tidb.git pr/29774:release-5.3-bc10104e05b0

---

Signed-off-by: joccau zak.zhao@pingcap.com

What problem does this PR solve?

Issue Number: close #29710

Problem Summary:
Append the prefix __TiDB_BR_Temporary_ into system database mysql multiply.
It causes restore failed because of incorrect schema name

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Backup system table before fix
[2021/11/12 14:30:15.438 +08:00] [INFO] [validate.go:78] ["checksum success"] [db=__TiDB_BR_Temporary___TiDB_BR_Temporary___TiDB_BR_Temporary_mysql] [table=person]

Backup and restore system table after fix
[2021/11/12 15:54:00.890 +08:00] [INFO] [validate.go:78] ["checksum success"] [db=__TiDB_BR_Temporary_mysql] [table=person]

[2021/11/12 16:12:22.328 +08:00] [INFO] [ddl.go:553] ["[ddl] start DDL job"] [job="ID:168, Type:rename table, State:none, SchemaState:queueing, SchemaID:3, TableID:123, RowCount:0, ArgLen:3, start time: 2021-11-12 16:12:22.229 +0800 CST, Err:<nil>, ErrCount:0, SnapshotVersion:0"] [query="RENAME TABLE__tidb_br_temporary_mysql.personTOmysql.person;"]

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• YuJuncen

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[ti-srebot]

/run-all-tests

[ti-srebot]

@joccau please accept the invitation then you can push to the cherry-pick pull requests. Comment with /cherry-pick-invite if the invitation is expired.
https://github.com/ti-srebot/tidb/invitations

[joccau]

/run-check_dev

[zhouqiang-cl]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 2da3d31

[joccau]

/run-check_dev