Lightning CSS: Sourcemap @include paths not updated

When I use the `--sourcemap` argument in the CLI to generate the CSS builds with sourcemaps, when the CSS uses `@include`, it does not update the path and therefore will not work.

In the code below, the builds are stored in the *dist* directory, while the CSS source code is stored in the *src* directory.

This is my simple code to reproduce this...
```
- src/
- stylesheet.css
- dist
- my-package.css
- my-package.css.map
- demo.html
- bundle.css
- package.json
```

bundle.css
```
@import 'src/stylesheet.css';
```

demo.html
```
<link rel="stylesheet" href="dist/my-package.css">
```

package.json
```
{
"name": "my-package",
"version": "1.0.0",
"license": "MIT",
"scripts": {
"build": "lightningcss --sourcemap bundle.css -o dist/my-package.css"
},
"devDependencies": {
"lightningcss-cli": "^1.25.1"
}
}
```

src/stylesheet.css
```
body {
background-color: red;
}
```

dist/my-package.css output
```
@import "src/stylesheet.css";

/*# sourceMappingURL=dist/my-package.css.map */
```

What I expected from the dist/my-package.css output
```
@import "../src/stylesheet.css";

/*# sourceMappingURL=dist/my-package.css.map */

```

Does anyone know why this is the outcome? Any help will be most appreciated.