### 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 (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_MOTION_VECTORS) {
		p_render_data->scene_data->calculate_motion_vectors = true;
	} else if (!is_reflection_probe && rb->get_use_taa()) {
		p_render_data->scene_data->calculate_motion_vectors = true;
	} else {
		p_render_data->scene_data->calculate_motion_vectors = false;
	}
	
	p_render_data->scene_data->directional_light_count = 0;
	p_render_data->scene_data->opaque_prepass_threshold = 0.99f;
	Size2i screen_size;
	RID color_framebuffer;
	RID color_only_framebuffer;
	RID depth_framebuffer;
	PassMode depth_pass_mode = PASS_MODE_DEPTH;
	uint32_t color_pass_flags = 0;
	Vector<Color> depth_pass_clear;
	bool using_separate_specular = false;
	bool using_ssr = false;
	bool using_sdfgi = false;
	bool using_voxelgi = false;
	bool reverse_cull = p_render_data->scene_data->cam_transform.basis.determinant() < 0;
	bool using_ssil = !is_reflection_probe && p_render_data->environment.is_valid() && environment_get_ssil_enabled(p_render_data->environment);
	if (is_reflection_probe) {
		uint32_t resolution = light_storage->reflection_probe_instance_get_resolution(p_render_data->reflection_probe);
		screen_size.x = resolution;
		screen_size.y = resolution;
		color_framebuffer = light_storage->reflection_probe_instance_get_framebuffer(p_render_data->reflection_probe, p_render_data->reflection_probe_pass);
		color_only_framebuffer = color_framebuffer;