Fix s3cmd deploy on ubuntu-latest

[cwillisf]

Changes:

• Move the ci-cd.yml workflow back to ubuntu-latest (see fix: reintroduce ubuntu-22 as workflow version #9127)
• Use s3cmd version 2.4.0 (current latest) and Python 3.12 (the latest Python that is officially compatible with s3cmd 2.4.0)

Reasoning:

GHA's ubuntu-latest tag recently moved from Ubuntu 22 to Ubuntu 24. GHA's ubuntu-24.04 image includes several versions of Python, but it defaults to Python 3.12 (and does not include Python 3.5). This caused our deploys to stop working for at least two reasons:

1. We were installing pip via a script that was designed specifically for Python 3.5
   • The script was downloaded from this hard-coded URL: https://bootstrap.pypa.io/pip/3.5/get-pip.py
   • This script is no longer compatible with Python 3.12
2. We were installing pip version 21.0.1, specifically
3. We were then using pip to install s3cmd at version 2.3.0, specifically
   • This version of s3cmd is no longer compatible with Python 3.12

We fixed the pip installation issue with #9123, which exposed the s3cmd incompatibility.

For the sake of getting our in-progress deploy to work, we temporarily specified ubuntu-22.04 (see #9127).

The changes in this new PR move ci-cd.yml back to Unbuntu 24 by changing runs-on back to ubuntu-latest. We still use the setup-python action as introduced by #9123, but we now specify Python 3.12 exactly. We also get pip for free.

Upgrading s3cmd to version 2.4.0 adds Python 3.12 compatibility. Combined with Python 3.12 from above, this means our deploys should work again.