WooCommerce Shipment Tracking 2.6.0

* Tweak - WooCommerce 9.9 compatibility.

* Replace ubuntu-20.04 with ubuntu-latest in GitHub Actions.
* Update Requires headers for WooCommerce compatibility.

* Tweak - WooCommerce 9.7 compatibility.

* Tweak - WordPress 6.7 compatibility.

* Tweak - WordPress 6.6 compatibility.

* Fix - Ensure API is loaded.
* Tweak - Bump tested WooCommerce version to 9.0 and minimum version to 8.8 (L-2 policy).

* Fix - Use local time when displaying the tracking date.

* Fix - Change Fan Courier Tracking URL.

* Fix - Allow custom tracking link to be empty.

* Fix - Custom tracking link not being formatted correctly.
* Fix - WordPress Coding Standards.