Fix sass importLoaders

[mariusc23]

This PR fixes the importLoaders setting for sass files. I believe this was broken in #5829 when an additional loader was introduced but the importLoaders setting was not incremented.

I ran into this trying to upgrade react-scripts locally. Verified this change fixes it for our project.

This is the error I ran into:

Error: resolve-url-loader: CSS error
  file:///MySassFile.module.scss:42:6: Unknown word
You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser
  You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser
    at runMicrotasks (<anonymous>)

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[ianschmitz]

Thanks!