Upgrade GitHub actions to Node 20

[query-jeremy]

The GitHub actions are using Node 16, which has been deprecated. GitHub records the following warning with each invokation:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/setup-python@v4. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

To resolve this, we just need to update the action.