### Godot version

4.1.1 stable

### System information

Windows 10

### Issue description

this is the default size loaded on startup 1024 which seems fine but it actually have loaded the default [2048] and ignored the size in project settings
![image](https://github.com/godotengine/godot/assets/53877170/c8c71de7-468a-487f-8e6c-dba1ce0f8fa5)

changing it now to any size will break it 
[2048]
![image](https://github.com/godotengine/godot/assets/53877170/3082ff09-b7d7-41f7-8fbb-813074a54135)

[512]
![image](https://github.com/godotengine/godot/assets/53877170/5ea4620f-52b5-4d0e-a5f5-747e777cd59d)


### Steps to reproduce

change 2d shadow atlas size in project settings while using compatibility renderer. 

### Minimal reproduction project

_
state.canvas_instance_batches[state.current_batch_index].instance_count++;
	r_index++;
	if (r_index >= data.max_instances_per_buffer) {
		
		
		glBindBuffer(GL_ARRAY_BUFFER, state.canvas_instance_data_buffers[state.current_data_buffer_index].instance_buffers[state.current_instance_buffer_index]);
#ifdef WEB_ENABLED
		glBufferSubData(GL_ARRAY_BUFFER, state.last_item_index * sizeof(InstanceData), sizeof(InstanceData) * r_index, state.instance_data_array);
#else
		
		void *buffer = glMapBufferRange(GL_ARRAY_BUFFER, state.last_item_index * sizeof(InstanceData), r_index * sizeof(InstanceData), GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT);
		memcpy(buffer, state.instance_data_array, r_index * sizeof(InstanceData));
		glUnmapBuffer(GL_ARRAY_BUFFER);
#endif
		_allocate_instance_buffer();
		r_index = 0;
		state.last_item_index = 0;
		r_batch_broken = false; 
		_new_batch(r_batch_broken);
		state.canvas_instance_batches[state.current_batch_index].start = 0;
	}
}
void RasterizerCanvasGLES3::_new_batch(bool &r_batch_broken) {