Netlify: select a new build image

[nate-double-u]

Notice from Netlify

After November 15, 2022, builds for this site will fail unless you update the build image.

[nate-double-u]

test build/deploy: https://app.netlify.com/sites/coredns/deploys/637d6d23ce1f1761e6acaeee

As builds have started to fail I've updated this. I don't see any maintainers or contributors in the Netlify team (https://app.netlify.com/sites/coredns/overview). We should make sure that there are some folks from the project on the Netlify team in case further changes need to be made.

Closing as complete.