fix(DesignTokens): Add missing dropdown token keys

mentioned in commit b2c2ef32

mentioned in merge request status-page!903

mentioned in merge request gitlab!184557 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4346 (merged)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1591 (merged)

mentioned in merge request gitlab!185040 (closed)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!67 (closed)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!367 (merged)