### 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)


u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
		if (ref_texture.is_valid()) {
			u.append_id(ref_texture);
		} else {
			u.append_id(texture_storage->texture_rd_get_default(RendererRD::TextureStorage::DEFAULT_RD_TEXTURE_CUBEMAP_ARRAY_BLACK));
		}
		uniforms.push_back(u);
	}
	{
		RD::Uniform u;
		u.binding = 4;
		u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
		RID texture;
		if (p_render_data && p_render_data->shadow_atlas.is_valid()) {
			texture = light_storage->shadow_atlas_get_texture(p_render_data->shadow_atlas);
		}
		if (!texture.is_valid()) {
			texture = texture_storage->texture_rd_get_default(RendererRD::TextureStorage::DEFAULT_RD_TEXTURE_DEPTH);
		}
		u.append_id(texture);
		uniforms.push_back(u);
	}
	{
		RD::Uniform u;
		u.binding = 5;
		u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
		if (p_use_directional_shadow_atlas && light_storage->directional_shadow_get_texture().is_valid()) {
			u.append_id(light_storage->directional_shadow_get_texture());
		} else {
			u.append_id(texture_storage->texture_rd_get_default(RendererRD::TextureStorage::DEFAULT_RD_TEXTURE_DEPTH));