fix(GlTable): removes border top when stacked

mentioned in commit b554f295

mentioned in merge request status-page!598 (merged)

mentioned in merge request gitlab!95710 (merged)

mentioned in merge request gitlab-docs!3046 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3017 (merged)

mentioned in merge request status-page!599 (merged)

mentioned in merge request gitlab!95922 (merged)

mentioned in merge request gitlab-docs!3063 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3030 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!87 (merged)