[Bug]: RawModule doesn't implement for module concatenation

### Version

```sh
N/A
```


### Details

https://github.com/web-infra-dev/rslib/pull/143/commits/6b7ba677740c84a04eb481f046ed6eb0df3a601c

The output `e2e/cases/resolve/__snapshots__/index.test.ts.snap` didn't go through concatenated logic.

### Reproduce link

https://github.com/web-infra-dev/rslib/pull/143/commits/6b7ba677740c84a04eb481f046ed6eb0df3a601c

### Reproduce Steps

N/A