### 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 (using_ssil) {
		RENDER_TIMESTAMP("Copy Final Framebuffer (SSIL)");
		_copy_framebuffer_to_ssil(rb);
	}
	RD::get_singleton()->draw_command_end_label();
	if (rb_data.is_valid() && taa && rb->get_use_taa()) {
		RENDER_TIMESTAMP("TAA")
		taa->process(rb, _render_buffers_get_color_format(), p_render_data->scene_data->z_near, p_render_data->scene_data->z_far);
	}
	if (rb_data.is_valid()) {
		_debug_draw_cluster(rb);
		RENDER_TIMESTAMP("Tonemap");
		_render_buffers_post_process_and_tonemap(p_render_data);
	}
	if (rb_data.is_valid()) {
		_render_buffers_debug_draw(rb, p_render_data->shadow_atlas, p_render_data->occluder_debug_tex);
		if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_SDFGI && rb->has_custom_data(RB_SCOPE_SDFGI)) {
			Ref<RendererRD::GI::SDFGI> sdfgi = rb->get_custom_data(RB_SCOPE_SDFGI);
			Vector<RID> view_rids;
			
			Size2i size = rb->get_internal_size();
			RID source_texture = rb->get_internal_texture();
			for (uint32_t v = 0; v < rb->get_view_count(); v++) {
				view_rids.push_back(rb->get_internal_texture(v));
			}
			sdfgi->debug_draw(p_render_data->scene_data->view_count, p_render_data->scene_data->view_projection, p_render_data->scene_data->cam_transform, size.x, size.y, rb->get_render_target(), source_texture, view_rids);
		}
	}
}
void RenderForwardClustered::_render_buffers_debug_draw(Ref<RenderSceneBuffersRD> p_render_buffers, RID p_shadow_atlas, RID p_occlusion_buffer) {