This updates nodejs from 18.17 to 20.12 since the former is nearing
end-of-life. In addition, the updates to npm and its node-gyp
dependencies will fix support for Python 3.12.

Note that we use v20.12.1 instead of v20.12.2 because the
latter doesn't appear to have a glibc-217 version yet:

* https://unofficial-builds.nodejs.org/download/release/v20.12.1/
* https://unofficial-builds.nodejs.org/download/release/v20.12.2/

Relates to:

* https://gitlab.com/gitlab-org/gitlab-development-kit/-/issues/2081
* https://gitlab.com/groups/gitlab-org/-/epics/13545

Changelog: changed