rspack unexpected css transform

reproduction steps:

1. Run pnpm build:webpack, see ./dist/main.css:

   body {
       background-color: rgba(0, 0, 0, 0.5);
   }

2. Run pnpm build:rspack, see ./dist/main.css:

   body{background-color:#00000080}
   /*# sourceMappingURL=main.css.map*/