Netlify deployment failing due to Ubuntu 16.04 Xenial pick

I have a repository where the Netlify deployment is consistently failing, e.g.
ENH: Set up correctly branches filter in build, test GHA workflow file by jhlegarreta · Pull Request #242 · carpentries-incubator/SDC-BIDS-dMRI · GitHub

It seems to be failing because it’s picking Ubuntu 16.04 Xenial:
Netlify App

Please read! End of support for Xenial build image: Everything you need to know

I have checked that the default Ubuntu in the project’s Netlify configuration is 18.04.

So what is missing here?

The link above shows two different sites deploys:

The first site above has been deleted but I do see that deploy used Xenial.

The other site above is using Focal and the build is failing because the version of Python being selected is not available.