Use semantic tokens in app/assets/stylesheets/components/rapid_diffs/diff_file_component.scss

See scan results at https://gitlab-org.gitlab.io/frontend/playground/gitlab-code-scanner/?search=check_id%20co%20%22color%22 for app/assets/stylesheets/components/rapid_diffs/diff_file_component.scss

diff_file_component.scss
File:
app/assets/stylesheets/components/rapid_diffs/diff_file_component.scss#L8
  border: 1px solid $gray-100;
diff_file_component.scss
File:
app/assets/stylesheets/components/rapid_diffs/diff_file_component.scss#L20
  color: $green-600;
diff_file_component.scss
File:
app/assets/stylesheets/components/rapid_diffs/diff_file_component.scss#L24
  color: $red-500;
diff_file_component.scss
File:
app/assets/stylesheets/components/rapid_diffs/diff_file_component.scss#L28
  border: 1px solid $gray-100;