PHP 8.3 Compatibility

[mikkamp]

Describe the issue:

The unit tests can be run with PHP 8.3 which confirms that the code (at least the part that's covered by unit tests) within the extension is compatible.

However one of the composer packages isn't fully compatible and we get the following deprecation notice:

PHP Deprecated:  Calling get_class() without arguments is deprecated in google-listings-and-ads/vendor/google/apiclient/src/Http/REST.php on line 58

There is already an opened issue for this and we are just waiting for the following PR to be resolved: googleapis/google-api-php-client#2509

Steps to reproduce:

1. Run the extension on a site with PHP 8.3 and WP debug logging on
2. View a page that sends a request to the Content API, like the Product Statuses page
3. Observe the deprecation notice in debug.log or on screen if configured to show notices there

Expected behavior:

No deprecation messages.