Support nightly, etc Node.js builds

[dominykas]

Ref: actions/setup-node#655

[ljharb]

I don't think there's much value here; the number of people on the planet that should be caring about these is barely past two digits.

[dominykas]

I'll see if I can add it in cheaply - shouldn't hurt too much.

Obviously opt-in.

[ljharb]

Sure, probably won’t hurt. I still haven’t added it to nvm and less then 20 people have ever brought it up ¯\_(ツ)_/¯