MAINTAINERS: Update nrf_hw_models project collaborators

Let's update this west module/project collaborators:
wopu-ot & thoh-ot have been out of the picture for these HW models for
quite a while now, while rugeGerritsen has been much more active.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>