Fix Sync Past Orders when HPOS Disabled

[n7studios]

Summary

Fixes this reported issue, due to this change, meaning that the Sync Past Orders functionality could determine which Orders need to be sent to Kit's purchase data API endpoint when WooCommerce's HPOS is not enabled (as was the case with this creator's site), resulting in it attempting to send all Orders.

Testing

• SyncPastOrdersHPOSCest: Renamed from SyncPastOrdersCest. Runs tests with HPOS enabled.
• SyncPastOrdersHPOSCLICest: Renamed from SyncPastOrdersCLICest. Run tests in CLI with HPOS enabled.
• SyncPastOrdersCest: Run tests with HPOS disabled.
• SyncPastOrdersCLICest: Run CLI tests with HPOS disabled.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)