### 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)


RID tex = gi.voxel_gi_instance_get_texture(p_voxel_gi_instances[i]);
				if (!tex.is_valid()) {
					tex = default_tex;
				}
				u.ids.write[i] = tex;
			} else {
				u.ids.write[i] = default_tex;
			}
		}
		uniforms.push_back(u);
	}
	{
		RD::Uniform u;
		u.binding = 8;
		u.uniform_type = RD::UNIFORM_TYPE_STORAGE_BUFFER;
		RID cb = p_cluster_buffer.is_valid() ? p_cluster_buffer : default_vec4_xform_buffer;
		u.append_id(cb);
		uniforms.push_back(u);
	}
	*/
	{
		RD::Uniform u;
		u.binding = 9;
		u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
		RID texture;
		if (rb.is_valid() && rb->has_texture(RB_SCOPE_BUFFERS, RB_TEX_BACK_DEPTH)) {
			texture = rb->get_texture(RB_SCOPE_BUFFERS, RB_TEX_BACK_DEPTH);
		} else if (is_multiview) {
			texture = texture_storage->texture_rd_get_default(RendererRD::TextureStorage::DEFAULT_RD_TEXTURE_2D_ARRAY_DEPTH);
		} else {