### 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
RendererRD::TextureStorage *texture_storage = RendererRD::TextureStorage::get_singleton();
	ERR_FAIL_COND(p_render_buffers.is_null());
	Ref<RenderBufferDataForwardClustered> rb_data = p_render_buffers->get_custom_data(RB_SCOPE_FORWARD_CLUSTERED);
	ERR_FAIL_COND(rb_data.is_null());
	RendererSceneRenderRD::_render_buffers_debug_draw(p_render_buffers, p_shadow_atlas, p_occlusion_buffer);
	RID render_target = p_render_buffers->get_render_target();
	if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_SSAO && p_render_buffers->has_texture(RB_SCOPE_SSAO, RB_FINAL)) {
		RID final = p_render_buffers->get_texture_slice(RB_SCOPE_SSAO, RB_FINAL, 0, 0);
		Size2i rtsize = texture_storage->render_target_get_size(render_target);
		copy_effects->copy_to_fb_rect(final, texture_storage->render_target_get_rd_framebuffer(render_target), Rect2(Vector2(), rtsize), false, true);
	}
	if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_SSIL && p_render_buffers->has_texture(RB_SCOPE_SSIL, RB_FINAL)) {
		RID final = p_render_buffers->get_texture_slice(RB_SCOPE_SSIL, RB_FINAL, 0, 0);
		Size2i rtsize = texture_storage->render_target_get_size(render_target);
		copy_effects->copy_to_fb_rect(final, texture_storage->render_target_get_rd_framebuffer(render_target), Rect2(Vector2(), rtsize), false, false);
	}
	if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_GI_BUFFER && p_render_buffers->has_texture(RB_SCOPE_GI, RB_TEX_AMBIENT)) {
		Size2i rtsize = texture_storage->render_target_get_size(render_target);
		RID ambient_texture = p_render_buffers->get_texture(RB_SCOPE_GI, RB_TEX_AMBIENT);
		RID reflection_texture = p_render_buffers->get_texture(RB_SCOPE_GI, RB_TEX_REFLECTION);
		copy_effects->copy_to_fb_rect(ambient_texture, texture_storage->render_target_get_rd_framebuffer(render_target), Rect2(Vector2(), rtsize), false, false, false, true, reflection_texture, p_render_buffers->get_view_count() > 1);
	}
}
void RenderForwardClustered::_render_shadow_pass(RID p_light, RID p_shadow_atlas, int p_pass, const PagedArray<RenderGeometryInstance *> &p_instances, const Plane &p_camera_plane, float p_lod_distance_multiplier, float p_screen_mesh_lod_threshold, bool p_open_pass, bool p_close_pass, bool p_clear_region, RenderingMethod::RenderInfo *p_render_info) {