### 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)


rb_data = rb->get_custom_data(RB_SCOPE_MOBILE);
		}
	}
	
	
	Vector<RD::Uniform> uniforms;
	{
		RD::Uniform u;
		u.binding = 0;
		u.uniform_type = RD::UNIFORM_TYPE_UNIFORM_BUFFER;
		u.append_id(scene_state.uniform_buffers[p_index]);
		uniforms.push_back(u);
	}
	{
		RID radiance_texture;
		if (p_radiance_texture.is_valid()) {
			radiance_texture = p_radiance_texture;
		} else {
			radiance_texture = texture_storage->texture_rd_get_default(is_using_radiance_cubemap_array() ? RendererRD::TextureStorage::DEFAULT_RD_TEXTURE_CUBEMAP_ARRAY_BLACK : RendererRD::TextureStorage::DEFAULT_RD_TEXTURE_CUBEMAP_BLACK);
		}
		RD::Uniform u;
		u.binding = 2;
		u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
		u.append_id(radiance_texture);
		uniforms.push_back(u);
	}
	{
		RID ref_texture = (p_render_data && p_render_data->reflection_atlas.is_valid()) ? light_storage->reflection_atlas_get_texture(p_render_data->reflection_atlas) : RID();
		RD::Uniform u;
		u.binding = 3;