Please add node 18 and (optionally) node 20 to testing

[mcm1957]

Please add github testing for node 18 (required for further releases) and (optionally) node 20.

Node 18 is the recommended node version. So testing must include node 18.

Thanks for your support.
McM1957

[git-kick]

Okay, @mcm1957, thank you for the hint, I will add Node 18 and Node 20.

[git-kick]

Done (master branch).