Proposed change:
Upgrade the versions of the actions/upload-artifact and actions/download-artifact actions to v4.

Motivation:
The version we're currently using for the actions/upload-artifact and actions/download-artifact actions (v3) is scheduled for deprecation on Nov 30, 2024.

This upgrade was attempted in #3487, but it failed because v4 of the action runs on node20, which doesn't work with Ubuntu 18.04.

We recently had to work around this issue with v3 through setting:

ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true

See #3322 for details.

To upgrade the versions, we'll either have to find a workaround that works with Ubuntu 18.04 or drop support for Ubuntu 18.04 and AL2.