the speed of fast-reorg add multiple indexes with multi-schema change is slower than fast-reorg=0

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. enable fast-reorg
2. disable tidb_enable_dist_task
3. alter table items add index index1 ((cast(col1 as char(253) array))), add index index2 ((cast(col2 as char(32) array)));

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

add index successfully and speed is faster than fast-reorg=0

3. What did you see instead (Required)

the speed is slower than fast-reorg=0

4. What is your TiDB version? (Required)

7.6.0