Enable new CSS compiler by default

After analyzing the CSS diff between the new and old compiler, the diff
doesn't have us concerned too much. We therefore want to enable the new
SASS compiler in CI/CD to see if there are any failures.

Furthermore we turn it on in development by default as well

- See also: https://gitlab.com/gitlab-org/gitlab/-/issues/438278
- Link to the Diff:
  https://gitlab.com/gitlab-org/frontend/playground/sass-compiler-diff/-/merge_requests/1#note_1758213709