### Godot version

4.0.rc6.mono.official

### System information

macOS 12.0.1

### Issue description

Just a minor visual issue.

When opening an empty directory the focus highlight is drawn incorrectly. It looks like the UI is drawing a smaller rectangle within the main rect:
<img width="1058" alt="Bildschirmfoto 2023-02-28 um 14 13 31" src="https://user-images.githubusercontent.com/11627131/221868794-7450606d-e758-4104-8f33-182d9779d7f8.png">


This behavior also changes when you hover over other items in the view, so I'm not sure if this a general issue with the focus highlighting or just an issue in the directory view:
<img width="1052" alt="Bildschirmfoto 2023-02-28 um 14 32 54" src="https://user-images.githubusercontent.com/11627131/221869308-4756f26e-cda2-4057-be1e-7439030895dc.png">


### Steps to reproduce

1. New Project
2. Browse
3. Create Folder
4. Click or Tab to set focus on the empty directory view

### Minimal reproduction project

N/A
GLuint new_buffers[3];
	glGenBuffers(3, new_buffers);
	
	glBindBuffer(GL_ARRAY_BUFFER, new_buffers[0]);
	GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_ARRAY_BUFFER, new_buffers[0], data.max_instance_buffer_size, nullptr, GL_STREAM_DRAW, "2D Batch UBO[" + itos(state.current_data_buffer_index) + "][0]");
	
	glBindBuffer(GL_UNIFORM_BUFFER, new_buffers[1]);
	GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_UNIFORM_BUFFER, new_buffers[1], sizeof(LightUniform) * data.max_lights_per_render, nullptr, GL_STREAM_DRAW, "2D Lights UBO[" + itos(state.current_data_buffer_index) + "]");
	
	glBindBuffer(GL_UNIFORM_BUFFER, new_buffers[2]);
	GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_UNIFORM_BUFFER, new_buffers[2], sizeof(StateBuffer), nullptr, GL_STREAM_DRAW, "2D State UBO[" + itos(state.current_data_buffer_index) + "]");
	state.current_data_buffer_index = (state.current_data_buffer_index + 1);
	DataBuffer db;
	db.instance_buffers.push_back(new_buffers[0]);
	db.light_ubo = new_buffers[1];
	db.state_ubo = new_buffers[2];
	db.last_frame_used = RSG::rasterizer->get_frame_number();
	state.canvas_instance_data_buffers.insert(state.current_data_buffer_index, db);
	state.current_data_buffer_index = state.current_data_buffer_index % state.canvas_instance_data_buffers.size();
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindBuffer(GL_UNIFORM_BUFFER, 0);
}
void RasterizerCanvasGLES3::_allocate_instance_buffer() {