### Godot version

v4.0.beta17.official [c40020513]

### System information

Windows 11, OpenGL (Compatibility), RTX 2060 (31.0.15.2824)

### Issue description

I tried to make a blurred panel for a ui element with texturelod via shader:

```glsl
shader_type canvas_item;

uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap_anisotropic;
uniform float blur_amount : hint_range(0.0, 5.0);

void fragment() {
	vec4 blurred = textureLod(SCREEN_TEXTURE, SCREEN_UV, blur_amount);
	COLOR = blurred;
}
```

but what I got instead is this:
![image](https://user-images.githubusercontent.com/72286622/217170426-49f6712d-47ef-4c53-b9f1-30d8ad868084.png)

vulkan renderer does not exhibit this issue:
![image](https://user-images.githubusercontent.com/72286622/217170565-a013c712-94f6-49d1-b9ec-091c28a7790b.png)


### Steps to reproduce

1. Add a TextureRect node
2. Add a Panel node to overlay the previously added node
3. Apply the blur shader to the panel node

### Minimal reproduction project

N/A
RenderTarget *rt = render_target_owner.get_or_null(p_render_target);
	ERR_FAIL_COND(!rt);
	ERR_FAIL_COND(rt->direct_to_screen);
	if (rt->backbuffer_fbo == 0) {
		_create_render_target_backbuffer(rt);
	}
	Rect2i region;
	if (p_region == Rect2i()) {
		region.size = rt->size;
	} else {
		region = Rect2i(Size2i(), rt->size).intersection(p_region);
		if (region.size == Size2i()) {
			return; 
		}
	}
	glDisable(GL_BLEND);
	
	glBindFramebuffer(GL_FRAMEBUFFER, rt->backbuffer_fbo);
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, rt->color);
	GLES3::CopyEffects::get_singleton()->copy_screen();
	if (p_gen_mipmaps) {
		GLES3::CopyEffects::get_singleton()->bilinear_blur(rt->backbuffer, rt->mipmap_count, region);
		glBindFramebuffer(GL_FRAMEBUFFER, rt->backbuffer_fbo);
	}
	glEnable(GL_BLEND); 
}
void TextureStorage::render_target_clear_back_buffer(RID p_render_target, const Rect2i &p_region, const Color &p_color) {