fix(stepper): impossible de changer le niveau de titre

CHANGELOG.md

...ponents/src/lib/components/stepper/stepper.component.html

...omponents/src/lib/components/stepper/stepper.component.ts

...dsfr-components/src/lib/components/stepper/stepper.e2e.ts

...r-components/src/lib/components/stepper/stepper.module.ts

...sfr-components/src/lib/components/stepper/stepper.spec.ts

...-components/src/lib/components/stepper/stepper.stories.ts

...rc/lib/shared/components/demo/demo-toolbar.component.html

...ts/src/lib/shared/components/heading/heading.component.ts

...-dsfr-components/src/lib/shared/properties/messages.en.ts

...-dsfr-components/src/lib/shared/properties/messages.fr.ts