bap3.yml pins pymc to 5.8.0, but there’s no associated pin on pymc-experimental, which is what I think is leading to this error. I’d just update everything to the latest versions if I were you – I’d rather deal with potential problems that would bring by learning the latest syntax (I can’t think of any major user-facing changing since then though).
If you’re not keen to do that, you need to pin pymc-experimental to whatever was out around version 5.8.0. That version was released September last year. Just checking the experimental releases, you can try 0.0.11 or 0.0.12. But again, I still recommend always going to the latest version.
cc @aloctavodia