WooCommerce Product Vendors 2.2.8

* Fix - Dev - Fix unit testin infrastructure.
* Fix - Dev - Remove default value from optional parameters that are followed by required parameters in functions/methods, since those are de-facto required and trigger a deprectation notice in PHP 8.
* Fix - Dev - Set PHP version to 7.2 in composer.json for compatibility with PHP 8.
* Tweak - WC 4.7 compatibility.
* Tweak - WP 5.5 compatibility.

* Fix - Multiple tax rates not calculating proper commission with Per Product Shipping.
* Tweak - Filters to allow multiple language versions of vendor data.
* Fix - Reporting stats for 'Last Month' are not accurate.
* Fix - Commas not properly escaped in CSV exports.
* Fix - Add wait time on Webhook creation failure before attempting to create new Webhook handler.

Fix – Replace deprecated jQuery methods.
Tweak – WordPress 5.5 compatibility.