fix(GlDisclosureDropdown): Prevent unwanted slot overrides in Vue 3

mentioned in commit d251faea

mentioned in merge request status-page!903

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

mentioned in merge request gitlab!147657 (merged)

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

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3787 (merged)