Refactor netlify/build tests to remove circular depndency through the test helpers

[lukasholzer]

currently it is impossible to do a partial migration to typescript from small packages as every tests introduces circular dependencies through packages/build/tests/helpers/config.js

https://github.com/netlify/build/blob/main/packages/build/tests/helpers/config.js#L8

This needs to be done first before continuing on the typescript migration