Upgrade bundled/requested node version to 20.16.0

[dannon]

Upgrades bundled/default node to the active LTS node v20. See release schedule here: https://nodejs.org/en/about/previous-releases

Node 18 is in maintenance mode for another 8 months or so, but by then 22 will be the active LTS.

Updates actions to use this. We could, instead, add multiple versions to the matrix but since we ship a specific version for compatibility we may just want to keep the tests focused?

How to test the changes?

(Select all options that apply)

• [ ] I've included appropriate automated tests.
• [ ] This is a refactoring of components with existing test coverage.
• [ ] Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• [x] I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[davelopez]

I think these 2 workflows should be updated too:

https://github.com/galaxyproject/galaxy/blob/19bc932db3a264caf237ff62484293b7d8bc4f2f/.github/workflows/jest.yaml#L19

https://github.com/galaxyproject/galaxy/blob/19bc932db3a264caf237ff62484293b7d8bc4f2f/.github/workflows/js_lint.yaml#L19

[dannon]

I think these 2 workflows should be updated too:

https://github.com/galaxyproject/galaxy/blob/19bc932db3a264caf237ff62484293b7d8bc4f2f/.github/workflows/jest.yaml#L19

https://github.com/galaxyproject/galaxy/blob/19bc932db3a264caf237ff62484293b7d8bc4f2f/.github/workflows/js_lint.yaml#L19

Good call, missed those in the grep for the specific 18.12.1

[dannon]

(draft while I tinker with github actions -- was trying to refactor so that we have a single setup-node composite action w/ a predefined or default version that we reuse, instead of copying it 10 times)

[github-actions[bot]]

This PR was merged without a "kind/" label, please correct.