Source

File: wp-includes/functions.php

function wp_get_direct_php_update_url() {
	$direct_update_url = '';

	if ( false !== getenv( 'WP_DIRECT_UPDATE_PHP_URL' ) ) {
		$direct_update_url = getenv( 'WP_DIRECT_UPDATE_PHP_URL' );
	}

	/**
	 * Filters the URL for directly updating the PHP version the site is running on from the host.
	 *
	 * @since 5.1.1
	 *
	 * @param string $direct_update_url URL for directly updating PHP.
	 */
	$direct_update_url = apply_filters( 'wp_direct_php_update_url', $direct_update_url );

	return $direct_update_url;
}