[CI][Integration] Use Node.js 20 by default

[kou]

Describe the enhancement requested

#46790 changed the default Node.js version in ci/docker/conda-integration.dockerfile but we don't use it as the default Node.js version. We're using NODE=18 in .env for the default Node.js version. So we should have updated .env too.

Component(s)

Continuous Integration, Integration

[kou]

Issue resolved by pull request 46821
#46821