fix: update light theme colors for text and background

mentioned in commit 61a42c51

mentioned in merge request status-page!903

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!28 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!300 (merged)

mentioned in merge request gitlab!148408 (merged)

mentioned in merge request gitlab!148674 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3792 (merged)

mentioned in commit kiran-4444/gitlab-ui@c0d0397e