Lightning physical import precheck failed due to only 3 out of 10 TiKVs have regions

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
1. Deploy 6.5 nightly TiDB cluster with 9 TiKVs and 6 TiFlash nodes.
2. Do lightning physical import

### 2. What did you expect to see? (Required)
Lighting import should succeed.

### 3. What did you see instead (Required)
Lighting precheck failed. There are 9 TiKVs nodes, but only 3 of them has regions


### 4. What is your TiDB version? (Required)

```
lightning-0:/# /tidb-lightning -V
Release Version: v6.5.0-nightly
Git Commit Hash: f096450c339152e583eb578912ddc0ef227125df
Git Branch: heads/refs/tags/v6.5.0-nightly
Go Version: go1.19.12
UTC Build Time: 2023-09-08 10:22:58
Race Enabled: false

/ # /tikv-server -V
TiKV
Release Version: 6.5.4
Edition: Community
Git Commit Hash: 6087ea61f99aaa9275d1834657d2d883736381cb
Git Commit Branch: heads/refs/tags/v6.5.5
UTC Build Time: 2023-09-09 06:47:09

mysql> SELECT tidb_version();
+------------------------------------------------------------
| tidb_version()
+------------------------------------------------------------
| Release Version: v6.5.5
Edition: Community
Git Commit Hash: 4237dd2511c872692998b89eb07c0f8890de14d8
Git Branch: heads/refs/tags/v6.5.5
UTC Build Time: 2023-09-08 09:50:00
GoVersion: go1.19.12
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: tikv |
+------------------------------------------------------------
1 row in set (0.00 sec)
```