### 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)


RendererRD::MeshStorage *mesh_storage = RendererRD::MeshStorage::get_singleton();
	RD::DrawListID draw_list = p_draw_list;
	RD::FramebufferFormatID framebuffer_format = p_framebuffer_Format;
	
	RD::get_singleton()->draw_list_bind_uniform_set(draw_list, render_base_uniform_set, SCENE_UNIFORM_SET);
	RD::get_singleton()->draw_list_bind_uniform_set(draw_list, p_params->render_pass_uniform_set, RENDER_PASS_UNIFORM_SET);
	RD::get_singleton()->draw_list_bind_uniform_set(draw_list, scene_shader.default_vec4_xform_uniform_set, TRANSFORMS_UNIFORM_SET);
	RID prev_material_uniform_set;
	RID prev_vertex_array_rd;
	RID prev_index_array_rd;
	RID prev_pipeline_rd;
	RID prev_xforms_uniform_set;
	bool should_request_redraw = false;
	bool shadow_pass = (p_params->pass_mode == PASS_MODE_SHADOW) || (p_params->pass_mode == PASS_MODE_SHADOW_DP);
	for (uint32_t i = p_from_element; i < p_to_element; i++) {
		const GeometryInstanceSurfaceDataCache *surf = p_params->elements[i];
		const RenderElementInfo &element_info = p_params->element_info[i];
		const GeometryInstanceForwardMobile *inst = surf->owner;
		if (inst->instance_count == 0) {
			continue;
		}
		uint32_t base_spec_constants = p_params->spec_constant_base_flags;
		
		GeometryInstanceForwardMobile::PushConstant push_constant;
		if (inst->store_transform_cache) {
			RendererRD::MaterialStorage::store_transform(inst->transform, push_constant.transform);
#ifdef REAL_T_IS_DOUBLE
			
			
			RendererRD::MaterialStorage::split_double(inst->transform.origin.x, &push_constant.transform[12], &push_constant.transform[3]);