build: include utilities.scss in published package

We noticed that the generate scss/utilities.scss isn't being published as part of the NPM package. This happens because the the publish job doesn't compile the lib itself, it actually depends on the build job's artifacts to get all the final files. These artifacts currently are:

      - public
      - dist
      - scss_to_js/scss_variables.*

This MR adds scss/utilities.scss to the list.

Since the publish job isn't triggered on development branches, the success here can be verified by downloading the artifact from the upload_artifacts job, which is similar to the publish job: https://gitlab.com/gitlab-org/gitlab-ui/-/jobs/318776973.

The archive does contain all SCSS files, including utilities.scss:

➜  Downloads tar -tvf gitlab-ui.package-include-utilities.tgz | grep scss/
-rw-r--r--  0 0      0         219 11 Oct 13:59 package/scss/README.md
-rw-r--r--  0 0      0        1119 11 Oct 13:59 package/scss/bootstrap.scss
-rw-r--r--  0 0      0        1703 11 Oct 13:59 package/scss/components.scss
-rw-r--r--  0 0      0        1111 11 Oct 13:59 package/scss/functions.scss
-rw-r--r--  0 0      0         255 11 Oct 13:59 package/scss/gitlab_ui.scss
-rw-r--r--  0 0      0         185 11 Oct 13:59 package/scss/mixins.scss
-rw-r--r--  0 0      0         325 11 Oct 13:59 package/scss/storybook.scss
-rw-r--r--  0 0      0       12797 11 Oct 13:51 package/scss/utilities.scss
-rw-r--r--  0 0      0       20963 11 Oct 13:59 package/scss/utility-mixins.scss
-rw-r--r--  0 0      0        6523 11 Oct 13:59 package/scss/variables.scss
-rw-r--r--  0 0      0         937 11 Oct 13:59 package/scss/variables_overrides.scss