Fix Taxonomy Attribute Mapping for Product Variations

[puntope]

Changes proposed in this Pull Request:

Closes #2071

• Adjusts WCProductAdapter::get_product_taxonomy method to return Parent terms as a fallback for taxonomies like product_tag, product_cat etc...
• Adding some tests covering this edge case

Detailed test instructions:

1. Follow the use case in Product tags not working with Google attributes on variable products #2071 and see it solved.

Additional details:

Changelog entry

Fix - Fix Taxonomy Attribute Mapping for Product Variations.

[martynmjones]

Hey @puntope, thanks for the quick fix 🙌

Tested locally and confirmed that the parent products terms will be used for variations as a fallback and the data successfully syncs with Merchant Center. So LGTM ✅

[sukafia]

@eason9487 I see the fix is ready. Is there a timeframe for rolling out the update?

[eason9487]

Hi @sukafia, I added this extension to the release schedule and expect to release it next Tuesday.