fix(css): replace gl-sm-border-l-none with gl-md-border-l-solid

mentioned in commit c5aeaac5

mentioned in merge request gitlab!64213 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2422 (merged)

mentioned in merge request status-page!307 (merged)

mentioned in merge request status-page!308 (merged)

mentioned in merge request gitlab-docs!1958 (merged)

mentioned in merge request gitlab-docs!1959 (closed)