Upgrade `actions/upload-artifact` to v4 and refactoring `pr-realm-js` workflow

[kraenhansen]

We're currently using actions/upload-artifact v3, which uses Node v16 and we're getting warnings on CI for this. As per the release notes for actions/upload-artifact@v4 it's suggested to follow this guide to perform the migration: https://github.com/actions/upload-artifact/blob/main/docs/MIGRATION.md

In its current form, no tests are initiated before prebuilds are uploaded for all platforms, which slows down the feedback loop when pushing changes to a PR branch. Since the upload-artifacts@v4 remove a feature we're depending on for this flow (implicit merging of artefacts that share name), we should take this opportunity to refactor our workflow into jobs where a test run only depends on the upload of the prebuilt artefact that it actually needs to complete.

In addition to this, we should consider optimising which prebuilds are actually produced and which tests we run:

• By default, I'd suggest we skip integration tests on all platforms except Node.js on Linux for PRs that touch only the platform independent code of our SDK.
• In addition to this default behaviour, we could signal a desire to run tests for additional platforms by adding specific platform labels to the PR.
• On release/... branches (and possibly merge commits to main) we build all artefacts and run tests on all platforms.

[sync-by-unito[bot]]

➤ PM Bot commented:

Jira ticket: RJS-2748

[kraenhansen]

https://github.com/realm/realm-js/issues/6446 seems related to this.

[kraenhansen]

If we choose to refactor the workflow such that test jobs depend on the upload of the prebuilt artifact that it actually needs, we could probably revert https://github.com/realm/realm-js/pull/5729 as well.