### 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)


}
				}
				if (lightmap_cull_index >= 0) {
					inst->gi_offset_cache = inst->lightmap_slice_index << 16;
					inst->gi_offset_cache |= lightmap_cull_index;
					flags |= INSTANCE_DATA_FLAG_USE_LIGHTMAP;
					if (scene_state.lightmap_has_sh[lightmap_cull_index]) {
						flags |= INSTANCE_DATA_FLAG_USE_SH_LIGHTMAP;
					}
					uses_lightmap = true;
				} else {
					inst->gi_offset_cache = 0xFFFFFFFF;
				}
			} else if (inst->lightmap_sh) {
				if (lightmap_captures_used < scene_state.max_lightmap_captures) {
					const Color *src_capture = inst->lightmap_sh->sh;
					LightmapCaptureData &lcd = scene_state.lightmap_captures[lightmap_captures_used];
					for (int j = 0; j < 9; j++) {
						lcd.sh[j * 4 + 0] = src_capture[j].r;
						lcd.sh[j * 4 + 1] = src_capture[j].g;
						lcd.sh[j * 4 + 2] = src_capture[j].b;
						lcd.sh[j * 4 + 3] = src_capture[j].a;
					}
					flags |= INSTANCE_DATA_FLAG_USE_LIGHTMAP_CAPTURE;
					inst->gi_offset_cache = lightmap_captures_used;
					lightmap_captures_used++;
					uses_lightmap = true;
				}
			}
		}