tidb-lightning table schema not found

## Bug Report

Please answer these questions before submitting your issue. Thanks!
tidb cluster not case sensitive for table and schema name. When the name of the imported file is uppercase and the name of the downstream database is lowercase, lightning will report an error

### 1. Minimal reproduce step (Required)
1. dumpling schema file name：
a
2. downstream schema name：
A
3. exec lightning import data to downstream from dumpling files

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

### 3. What did you see instead (Required)
a schema not found

### 4. What is your TiDB version? (Required)
tidb and tidb-lightning all versiion