multipleCheckOrNo has hardcoded string

On file picker activity there is a toast which uses a hardcoded string and not the provided one

```
listAdapter?.multipleCheckOrNo(item, position, ::isCanSelect) {
    Toast.makeText(
        this@FilePickerActivity.applicationContext,
        "最多只能选择 $maxSelectable 项",
        Toast.LENGTH_SHORT
    ).show()
}
```