fix(GlFilteredSearch): Make close button keyboard accessible

mentioned in commit 9367cc7b

mentioned in merge request gitlab!137802 (merged)

mentioned in merge request gitlab!138396 (closed)

mentioned in merge request status-page!888 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!243 (merged)

mentioned in merge request gitlab-docs!4447 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3641 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!21 (merged)