Mismatch unit of configuration item when set and then get config via SQL

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```SQL
set config tikv `raftstore.raft-entry-max-size`='24MB';

show config where type='tikv' and name ='raftstore.raft-entry-max-size';
```

### 2. What did you expect to see? (Required)
The output value should be consistent with the input '24MB';

### 3. What did you see instead (Required)
'24MiB'. In other words, MiB vs MB.

### 4. What is your TiDB version? (Required)
v7.5.1