br restore reported split region error when setting granularity=coarse-grained

[AkiraXie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. restore point with --granularity=coarse-grained
2. restore 2nd restore with checkpoints

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

pass

3. What did you see instead (Required)

Error: split region failed: err=message:"key 748000000000009FFF3F5F698000000000FF000001FB00000000FB is not in region key range [748000000000009EFF6A5F72FFFFFFFFFFFFFFFFFF0000000000FB, 748000000000009FFF3F5F698000000000FF000001FB00000000FB) for region 283948" key_not_in_region:<key:"t\200\000\000\000\000\000\237\377?_i\200\000\000\000\000\377\000\000\001\373\000\000\000\000\373" region_id:283948 start_key:"t\200\000\000\000\000\000\236\377j_r\377\377\377\377\377\377\377\377\377\000\000\000\000\000\373" end_key:"t\200\000\000\000\000\000\237\377?_i\200\000\000\000\000\377\000\000\001\373\000\000\000\000\373" > 
....

4. What is your TiDB version? (Required)

sh-5.1# /br --version
Release Version: v7.6.0
Git Commit Hash: 370b2d5
Git Branch: heads/refs/tags/v7.6.0
Go Version: go1.21.5
UTC Build Time: 2024-01-21 13:28:35
Race Enabled: false

[AkiraXie]

/severity major