Remove EoL and add new Node versions to Actions

[mimiflynn]

          Since EOL for Node 12 was April 30, 2022, and Node 14 was a year later, those checks can be removed from this project's build. To the same point, Node 20 could be added to the checks. Thoughts?

Originally posted by @mimiflynn in https://github.com/morganstanley/needle/issues/78#issuecomment-1813155470