Bug Report

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1. Minimal reproduce step (Required)

https://ci.pingcap.net/blue/organizations/jenkins/br_ghpr_unit_and_integration_test/detail/br_ghpr_unit_and_integration_test/16116/pipeline/125/

we ingest two times of github.com/pingcap/tidb/br/pkg/lightning/backend/local/failToSplit=2*return(""), and expected one engine trigger it twice. But in the failed test two engines each triggered it once.

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)