Maintenance: Ch. 9.x - non-normative content marked in an inconsistent way

https://simulation.pages.asam.net/-/openscenario/openscenario-antora-gen/-/jobs/77939/artifacts/public/ASAM_OpenSCENARIO_DSL/latest/user-guide/user-guide.html states that the whole chapter 9 is non-normative.

Chapter 9.1 is correctly marked, the non-normative parts have the gray background. Chapters 9.2 and 9.3 use ascidoctor rule to mark, which does not result in visible changes.

Solution: Rework 9.2 and 9.3 to have gray non-normative background