### Godot version

4.0.2 stable

### System information

issue tested on win10 with ryzen 7 and rx 6600, win11 with ryzen 7 and gtx 3050

### Issue description

When creating a screen reading post processing shader, the normal buffer functions correctly in the editor, but does not seem to be functioning as expected in debug, producing only a solid colour when run. I am unsure if this behaviour is intended, but if so, I feel it should be properly documented.

Running correctly in editor:
![image](https://user-images.githubusercontent.com/71034402/230672620-fc5e4baf-c12e-4755-b7a2-206087459307.png)

Solid colour in debug:
![image](https://user-images.githubusercontent.com/71034402/230672489-d9c29755-c2d3-4e72-9ea0-355148e916fe.png)


### Steps to reproduce

*this shader should be attached to a MeshInstance3D quadmesh*
minimal shader to reproduce:

```glsl
shader_type spatial;
render_mode unshaded, cull_disabled;

uniform sampler2D NORMAL_TEXTURE : hint_normal_roughness_texture, filter_linear_mipmap;

void vertex(){
	VERTEX *= 2.0;
	POSITION = vec4(VERTEX, 1.0);
}

void fragment(){
	ALBEDO = texture(NORMAL_TEXTURE, SCREEN_UV).rgb;
}
```

### Minimal reproduction project

N/A
if (p_render_buffers.is_valid() && current_cluster_builder != nullptr) {
		RS::ViewportDebugDraw dd = get_debug_draw_mode();
		if (dd == RS::VIEWPORT_DEBUG_DRAW_CLUSTER_OMNI_LIGHTS || dd == RS::VIEWPORT_DEBUG_DRAW_CLUSTER_SPOT_LIGHTS || dd == RS::VIEWPORT_DEBUG_DRAW_CLUSTER_DECALS || dd == RS::VIEWPORT_DEBUG_DRAW_CLUSTER_REFLECTION_PROBES) {
			ClusterBuilderRD::ElementType elem_type = ClusterBuilderRD::ELEMENT_TYPE_MAX;
			switch (dd) {
				case RS::VIEWPORT_DEBUG_DRAW_CLUSTER_OMNI_LIGHTS:
					elem_type = ClusterBuilderRD::ELEMENT_TYPE_OMNI_LIGHT;
					break;
				case RS::VIEWPORT_DEBUG_DRAW_CLUSTER_SPOT_LIGHTS:
					elem_type = ClusterBuilderRD::ELEMENT_TYPE_SPOT_LIGHT;
					break;
				case RS::VIEWPORT_DEBUG_DRAW_CLUSTER_DECALS:
					elem_type = ClusterBuilderRD::ELEMENT_TYPE_DECAL;
					break;
				case RS::VIEWPORT_DEBUG_DRAW_CLUSTER_REFLECTION_PROBES:
					elem_type = ClusterBuilderRD::ELEMENT_TYPE_REFLECTION_PROBE;
					break;
				default: {
				}
			}
			current_cluster_builder->debug(elem_type);
		}
	}
}
void RenderForwardClustered::_update_volumetric_fog(Ref<RenderSceneBuffersRD> p_render_buffers, RID p_environment, const Projection &p_cam_projection, const Transform3D &p_cam_transform, const Transform3D &p_prev_cam_inv_transform, RID p_shadow_atlas, int p_directional_light_count, bool p_use_directional_shadows, int p_positional_light_count, int p_voxel_gi_count, const PagedArray<RID> &p_fog_volumes) {