gift-card-settings-tab.php

<?php
add_filter( 'woocommerce_product_data_tabs', 'gift_card_tab' );

function gift_card_tab( $tabs) {
	// Key should be exactly the same as in the class product_type
	$tabs['gift_card'] = array(
		'label'	 => __( 'Gift Card', 'wcpt' ),
		'target' => 'gift_card_options',
		'class'  => ('show_if_gift_card'),
	);
	return $tabs;
}