fix(GlDropdownItem): Fix dropdown item disabled state styling

mentioned in commit 77401fd3

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!104 (merged)

mentioned in merge request status-page!654 (closed)

mentioned in merge request gitlab!105756 (merged)

mentioned in merge request status-page!655 (merged)

mentioned in merge request gitlab!105860 (merged)

mentioned in merge request gitlab-docs!3335 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3172 (merged)

mentioned in commit 7868f22c

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3180 (merged)