Add Iceland to the WooCommerce list of countries that use VAT

add_iceland_to_vat_countries.php

<?php

declare(strict_types = 1);

/*
Add Iceland to the WooCommerce list of countries that use VAT

A PR has been sent over to the WooCommerce codebase, at
https://github.com/woocommerce/woocommerce/pull/62126 but it
is unlikely to result in any concrete results and has not been
looked at as of this wrting.
*/
add_filter(
	'woocommerce_vat_countries',
	function ( array $countries ): array {
		if ( key_exists( 'IS', $countries ) ) {
			return $countries;
		}

		return array_merge( $countries, array( 'IS' ) );
	},
	10,
	1
);