[Bug]: output.sourceMap.css: true does not take effect

[Timeless0911]

Version

System:
    OS: macOS 14.6.1
    CPU: (10) arm64 Apple M1 Max
    Memory: 701.70 MB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Browsers:
    Chrome: 131.0.6778.265
    Safari: 17.6
  npmPackages:
    @rsbuild/core: ^1.1.8 => 1.1.13 
    @rsbuild/plugin-react: ^1.0.7 => 1.1.0

Details

output.sourceMap.css: true does not take effect when output.sourceMap.js: false.

When I configure output.sourceMap.js with values like cheap-source-map, it works well.

Reproduce link

basic react demo

Reproduce Steps

1. Create a basic React project via npm create rsbuild@latest
2. Add configuration like:

import { defineConfig } from "@rsbuild/core";
import { pluginReact } from "@rsbuild/plugin-react";

export default defineConfig({
+  output: {
+   sourceMap: {
+      css: true,
+    },
+ },
  plugins: [pluginReact()],
});