the same task run on different BRs at the same time when BR use checkpoint mode

[Leavrth]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. run BR
2. run another BR with the same parameter

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

1. the second BR runs failed　

3. What did you see instead (Required)

2. the second BR runs successfully

4. What is your TiDB version? (Required)

master/v6.5.0