ssgilightmap: make example qmllint clean

- Use the typed view.currentScene instead of the untyped
  Loader3D item when toggling enableLightmaps
- Add .qmllint.ini with MaxWarnings=0

Tested changes by running the example and pressing the changed buttons.

Pick-to: 6.12
Task-number: QTBUG-134589
Change-Id: Iadb8fbd4b2a56ad4cf0284cb7fc4206ec7ec2443
Reviewed-by: Jonas Karlsson <jonas.karlsson@qt.io>