### 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)


light_projectors_get_filter() == RS::LIGHT_PROJECTOR_FILTER_LINEAR_MIPMAPS_ANISOTROPIC;
	spec_constants.push_back(sc);
	scene_shader.set_default_specialization_constants(spec_constants);
	base_uniforms_changed(); 
}
RenderForwardMobile::RenderForwardMobile() {
	singleton = this;
	sky.set_texture_format(_render_buffers_get_color_format());
	String defines;
	defines += "\n#define MAX_ROUGHNESS_LOD " + itos(get_roughness_layers() - 1) + ".0\n";
	if (is_using_radiance_cubemap_array()) {
		defines += "\n#define USE_RADIANCE_CUBEMAP_ARRAY \n";
	}
	
	defines += "\n#define MAX_DIRECTIONAL_LIGHT_DATA_STRUCTS " + itos(MAX_DIRECTIONAL_LIGHTS) + "\n";
	{
		
		scene_state.max_lightmaps = 2;
		defines += "\n#define MAX_LIGHTMAP_TEXTURES " + itos(scene_state.max_lightmaps) + "\n";
		defines += "\n#define MAX_LIGHTMAPS " + itos(scene_state.max_lightmaps) + "\n";
		scene_state.lightmap_buffer = RD::get_singleton()->storage_buffer_create(sizeof(LightmapData) * scene_state.max_lightmaps);
	}
	{
		
		scene_state.max_lightmap_captures = 2048;
		scene_state.lightmap_captures = memnew_arr(LightmapCaptureData, scene_state.max_lightmap_captures);
		scene_state.lightmap_capture_buffer = RD::get_singleton()->storage_buffer_create(sizeof(LightmapCaptureData) * scene_state.max_lightmap_captures);
	}
	{
		defines += "\n#define MATERIAL_UNIFORM_SET " + itos(MATERIAL_UNIFORM_SET) + "\n";