Lighten border subtle in dark mode.

feat(Borders): Update subtle dark

See merge request gitlab-org/gitlab-ui!4844



Merged-by: Scott de Jonge <sdejonge@gitlab.com>
Approved-by: Scott de Jonge <sdejonge@gitlab.com>
Approved-by: Sascha Eggenberger <seggenberger@gitlab.com>
Co-authored-by: GitLab Bot <gitlab-bot@gitlab.com>
Co-authored-by: Jeremy Elder <jelder@gitlab.com>

# [103.7.0](gitlab-org/gitlab-ui@v103.6.1...v103.7.0) (2024-11-26)

### Features

* **Borders:** Update subtle dark ([ff7d79d1](gitlab-org/gitlab-ui@ff7d79d1))