feat(checkbox): Fix disabled custom control color

mentioned in commit 3b84cba1

mentioned in merge request gitlab!85109 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2824 (merged)

mentioned in merge request status-page!495 (merged)

mentioned in merge request gitlab!85596 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2825 (merged)

mentioned in merge request gitlab-docs!2598 (merged)

mentioned in merge request gitlab-docs!2600 (closed)