change to node20 for all actions

[nickfyson]

This PR upgrades all the actions to use node20, and bumps the major version to v3.

It also adds a new PR check to confirm the consistency of node versions across all actions, and ensure that we do not change this version in backport PRs to older releases.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.
• Confirm the changelog has been updated if necessary.

[github-actions]

Pushed a commit to update the checked-in dependencies. Please mark the PR as ready for review to trigger PR checks.

[aeisenberg]

I think the changes you made are good for bumping the node version of the actions. However, once we merge this, we can no longer release v2 of the action until we also update the release scripts to what we had before when we released v1 and v2 (now will be v2 and v3). That's a dicey state to be in.

So, either we can recreate the release scripts and merge it first, or we do them at the same time. I can't remember how we did it last time.

[aeisenberg]

Right...it was this PR that added the v2->v1->main release steps #995. It was merged before the node version changes were merged in #1000.

[aeisenberg]

This PR #1482 is the revert PR that removed the v1 release process.

[github-actions]

Pushed a commit to update the checked-in dependencies. Please mark the PR as ready for review to trigger PR checks.

[henrymercer]

Looks good. Let's wait for the CodeQL 2.15.4 release to complete before merging this to reduce the risk of that release.

One potential safety check we could add is a PR check that fails if the release branch is v2 and the Node version of any Actions is Node 20. This could help make sure (a) we don't forget to switch the v2 branch back to running on node16 the first time we release it, and (b) any new Action we add to main runs on node16 in the v2 branch.

[henrymercer]

Minor suggestions to the new PR check, looks good overall :)

[nickfyson]

NB – The introduction of a matrix for the Check JS job means that Check JS has been replaced by Check JS (16.11) and Check JS (current).

Once this PR is approved and ready to merge I will remove Check JS as a required check, and once merged I will run the update-required-checks.sh script in order to make the new checks required.