lightning import stuck when PD/TiKV has label

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
1) deploy tidb in 6 machines, 128c256G,tidb v7.3.0
2) 1 tidb+2 tikv every machine(2 tikv get lable host1/host2)
3)lightning impot csv is slow
4)see lightning log and pd-ctl, always scattering or split region;
5) csv max size is 4GiB,total 20~30GiB,about 1000 tables;
6)then we use tidb-lightning v7.1.0 import tidb v7.3.0,but still get same problem;
7)we deploy tidb v7.1.0,and use tidb-lightning v7.1.0 import csv,still get same problem;
8) finally,we delete pd and tikv label,use tidb-lightning v7.1.0 import csv to tidb v7.1.0, it's fast;

### 2. What did you expect to see? (Required)
1)lightning should not always scattering or split region;
2) fast import csv into tidb;

### 3. What did you see instead (Required)
1)always scattering or split region;

### 4. What is your TiDB version? (Required)
v7.3.0 & v7.1.0