### Godot version

4.0 Stable

### System information

Ubuntu 22.04

### Issue description

Setting fog_affect_sky = 1 do not have the desired effect when using a Color sky mode. It works properly if we use a procedural sky or the forward+ renderer.

![Screenshot from 2023-03-03 16-50-53](https://user-images.githubusercontent.com/8985409/222870514-0195c4cb-bbca-4e9b-bb6a-6e2a568d2f7b.png)


### Steps to reproduce

Add a sky with a plain color mode like the Clear Color default option. Enable fog and set fog_affect_sky value to 1. Sky is still not affected by fog. 

### Minimal reproduction project
[mobile_fog_sky_bug.zip](https://github.com/godotengine/godot/files/10887265/mobile_fog_sky_bug.zip)


shader_version = SceneShaderForwardMobile::SHADER_VERSION_SHADOW_PASS_DP;
			} break;
			case PASS_MODE_DEPTH_MATERIAL: {
				ERR_FAIL_COND_MSG(p_params->view_count > 1, "Multiview not supported for material pass");
				shader_version = SceneShaderForwardMobile::SHADER_VERSION_DEPTH_PASS_WITH_MATERIAL;
			} break;
		}
		PipelineCacheRD *pipeline = nullptr;
		pipeline = &shader->pipelines[cull_variant][primitive][shader_version];
		RD::VertexFormatID vertex_format = -1;
		RID vertex_array_rd;
		RID index_array_rd;
		
		if (surf->owner->mesh_instance.is_valid()) {
			mesh_storage->mesh_instance_surface_get_vertex_arrays_and_format(surf->owner->mesh_instance, surf->surface_index, pipeline->get_vertex_input_mask(), vertex_array_rd, vertex_format);
		} else {
			mesh_storage->mesh_surface_get_vertex_arrays_and_format(mesh_surface, pipeline->get_vertex_input_mask(), vertex_array_rd, vertex_format);
		}
		index_array_rd = mesh_storage->mesh_surface_get_index_array(mesh_surface, element_info.lod_index);
		if (prev_vertex_array_rd != vertex_array_rd) {
			RD::get_singleton()->draw_list_bind_vertex_array(draw_list, vertex_array_rd);
			prev_vertex_array_rd = vertex_array_rd;
		}
		if (prev_index_array_rd != index_array_rd) {
			if (index_array_rd.is_valid()) {
				RD::get_singleton()->draw_list_bind_index_array(draw_list, index_array_rd);
			}
			prev_index_array_rd = index_array_rd;
		}
		RID pipeline_rd = pipeline->get_render_pipeline(vertex_format, framebuffer_format, p_params->force_wireframe, p_params->subpass, base_spec_constants);