need to check if lightning package can find new leader when TiKV down during `ingest` function

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

during `ingest` function running, the connected region leader TiKV node is down

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

after retry, lightning can make progress

### 3. What did you see instead (Required)

TBD

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