### Godot version

4.2.dev3.official

### System information

Windows 10 - GLES3 (Compatibility)

### Issue description

When a text is typed into the SpinBox node, and the `Enter` key is pressed, the text is normally removed, and the last valid number value of the SpinBox is restored.
However, when the string that is input is `"Nil"`, pressing `Enter` won't remove it, as it would do with any other text.

https://github.com/godotengine/godot/assets/141344817/a866a597-02db-4195-b45e-87578e0f1f92

### Steps to reproduce

0. Create a new project.
1. Add SpinBox node.
2. Run the project.
3. Input any valid number into the SpinBox.
4. Try to input some text into the SpinBox.
5. Try to type and input "Nil" text into the SpinBox.

### Minimal reproduction project

[SpinBox Nil - MRP.zip](https://github.com/godotengine/godot/files/12453969/SpinBox.Nil.-.MRP.zip)

} break;
		case NOTIFICATION_EXIT_TREE: {
			_release_mouse();
		} break;
		case NOTIFICATION_TRANSLATION_CHANGED: {
			queue_redraw();
		} break;
		case NOTIFICATION_THEME_CHANGED: {
			call_deferred(SNAME("update_minimum_size"));
			get_line_edit()->call_deferred(SNAME("update_minimum_size"));
		} break;
		case NOTIFICATION_LAYOUT_DIRECTION_CHANGED: {
			queue_redraw();
		} break;
	}
}
void SpinBox::set_horizontal_alignment(HorizontalAlignment p_alignment) {
	line_edit->set_horizontal_alignment(p_alignment);
}
HorizontalAlignment SpinBox::get_horizontal_alignment() const {
	return line_edit->get_horizontal_alignment();
}
void SpinBox::set_suffix(const String &p_suffix) {
	if (suffix == p_suffix) {
		return;
	}
	suffix = p_suffix;
	_update_text();
}
String SpinBox::get_suffix() const {