Pipeline editor: Add hidden h1

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183828



Merged-by: Florie Guibert <fguibert@gitlab.com>
Approved-by: Chad Lavimoniere <clavimoniere@gitlab.com>
Approved-by: Florie Guibert <fguibert@gitlab.com>
Co-authored-by: Sascha Eggenberger <seggenberger@gitlab.com>