UPDATE: Well, I've still not received that email from Google and, when I log into my Gsuite admin account, it's still showing "You are on the G Suite legacy free-of-charge edition. Consider upgrading to Google Workspace Business Starter." at the top of the Admin Console page. And, underneath:

Plan details

Payment plan -- Free plan

Licences -- 88 available, 12 assigned

Estimated monthly bill --Free edition (no charges)

So, either that article was a spoof, or Google are rolling this out gradually.