Thank you Magnus. Given that I had all of the others switched over to send directly to gmail I didn't really think to check the old Yahoo! account.
So unless you can find it in some trash/spam folder in yahoo, then they have simply decided to eat it without letting you or us know. I bet if you look carefully, you may see a similar pattern on pgsql-novice which is also subscribed with that address.
I'm unsure how to unsubscribe those now that my community account only knows about my newer gmail address. I've subscribed both of those to my gmail, are you able to unsubscribe the yahoo address from any/all lists?
In the end, unless you have a strong reason to want to keep that one on a separate email address, I would advise you to unsubscribe the yahoo address and resubscribe with your gmail address. Yahoo are notoriously terrible at actually delivering email, so I'm not entirely surprised at this happening specifically to a yahoo address...
These did end up in the junk folder in my Yahoo! account - which I never check since I forward all of the good email from there to gmail.