fix(GlDropdown): Wrap text in dropdown section header

mentioned in commit e2215bcd

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2746 (closed)

mentioned in merge request status-page!473 (merged)

mentioned in merge request gitlab!82590 (closed)

mentioned in commit 5f29ea72

mentioned in merge request gitlab-docs!2490 (merged)

mentioned in merge request gitlab!83216 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2755 (merged)