Add support for PHP 8.x

Hi Tabby team 👋,

After updating my site to PHP 8.1 (with WordPress 6.x and WooCommerce), I noticed the following warning in my error logs when placing an order:

PHP Warning: WC_Tabby::woocommerce_checkout_order_processed(): Argument #3 ($order) must be passed by reference, value given in /home/xxxx/public_html/wp-includes/class-wp-hook.php on line 324 Root cause

In your plugin file:
/wp-content/plugins/tabby-checkout/includes/class-wc-tabby.php

The function is currently defined as:

public function woocommerce_checkout_order_processed( $order_id, $posted_data, &$order ) { ... }

WooCommerce passes the $order object by value, not by reference.
PHP 8.x is stricter and throws a warning because of the & (pass-by-reference). Suggested fix

Simply remove the reference & in the function definition:

public function woocommerce_checkout_order_processed( $order_id, $posted_data, $order ) { ... }

This change makes the plugin compatible with PHP 8+ and WooCommerce’s current hook signature. ⚠️ Notes

• The warning doesn’t break checkout, but it clutters error logs.
• It’s best to patch this in the official release, so users don’t have to manually edit plugin files.