Update to Node 20

[ajyong]

I'm still piecing together our tooling, but I think the scope of work here is:

• Change .nvmrc
• Ensure GitHub actions stop failing just because we use an old, unsupported Node version

Is the above missing anything?

[arashsheyda]

@ajyong the .nvmrc is for developing locally, the workflow is already on node 20 but somehow sometimes it's doing weied things (like adding unuseful things to package.json)