dummy_rasterizer now returns lightmap type

Previously VS::INSTANCE_NONE was returned for Lightmap data, this caused `visual_server_scene.cpp` to assert in `instance_set_use_lightmap()`

Now `dummy_rasterizer.h` returns `VS::INSTANCE_LIGHTMAP_CAPTURE` for lightmap capture data thus satisfying `visual_server_scene`

drivers/dummy/rasterizer_dummy.h

@@ -719,6 +719,8 @@ public:
 	VS::InstanceType get_base_type(RID p_rid) const {
 		if (mesh_owner.owns(p_rid)) {
 			return VS::INSTANCE_MESH;
+		} else if (lightmap_capture_data_owner.owns(p_rid)) {
+			return VS::INSTANCE_LIGHTMAP_CAPTURE;
 		}
 
 		return VS::INSTANCE_NONE;