### 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::LightStorage *light_storage = RendererRD::LightStorage::get_singleton();
	RendererRD::MaterialStorage *material_storage = RendererRD::MaterialStorage::get_singleton();
	if (render_base_uniform_set.is_null() || !RD::get_singleton()->uniform_set_is_valid(render_base_uniform_set) || (lightmap_texture_array_version != light_storage->lightmap_array_get_version())) {
		if (render_base_uniform_set.is_valid() && RD::get_singleton()->uniform_set_is_valid(render_base_uniform_set)) {
			RD::get_singleton()->free(render_base_uniform_set);
		}
		
		lightmap_texture_array_version = light_storage->lightmap_array_get_version();
		Vector<RD::Uniform> uniforms;
		{
			RD::Uniform u;
			u.binding = 2;
			u.uniform_type = RD::UNIFORM_TYPE_SAMPLER;
			u.append_id(scene_shader.shadow_sampler);
			uniforms.push_back(u);
		}
		{
			RD::Uniform u;
			u.binding = 3;
			u.uniform_type = RD::UNIFORM_TYPE_SAMPLER;
			RID sampler;
			switch (decals_get_filter()) {
				case RS::DECAL_FILTER_NEAREST: {
					sampler = material_storage->sampler_rd_get_default(RS::CANVAS_ITEM_TEXTURE_FILTER_NEAREST, RS::CANVAS_ITEM_TEXTURE_REPEAT_DISABLED);
				} break;
				case RS::DECAL_FILTER_LINEAR: {
					sampler = material_storage->sampler_rd_get_default(RS::CANVAS_ITEM_TEXTURE_FILTER_LINEAR, RS::CANVAS_ITEM_TEXTURE_REPEAT_DISABLED);
				} break;
				case RS::DECAL_FILTER_NEAREST_MIPMAPS: {