CSS pre-processor config does not respect sourceMap flag

[mdziekon]

Describe the bug

In current version of react-scripts (CRA 5.0.1), it seems disabling source maps generation (with GENERATE_SOURCEMAP=false env) is not respected when configuring certain pre-processors (such as sass-loader).
It's quite an easy thing to fix, as it boils down to a hardcoded value of true when setting up the pre-processors config here:
https://github.com/facebook/create-react-app/blob/main/packages/react-scripts/config/webpack.config.js#L188-L193

I'm going to submit a fix for that, but since CRA is essentially "development-dead", I'm pretty sure no one is going to pick that PR up, but it's still worth a try, or to serve as a hotfix for those who forked CRA or use tools like Craco to modify CRA config.

Steps to reproduce

1. Build your project with GENERATE_SOURCEMAP=false env variable set

Expected behavior

• No source maps are included

Actual behavior

• SCSS-related source maps are included

[mdziekon]

Sorry, my bad, I didn't notice that resolve-url-loader loader requires this flag to be set to true.