Update the publish workflow example

[LukeCarrier]

Fix a bunch of node.js deprecations in the example GitHub Actions workflow.

Deprecations:

• Node.js 16 actions:
  • actions/checkout@v3 -> actions/checkout@v4
  • actions/configure-pages@v1 -> actions/configure-pages@v5
  • actions/setup-python@v2 -> actions/setup-python@v5
• Node.js 12 actions forced to run on 16:
  • actions/setup-python@v2 -> actions/setup-python@v5
• Invalid environment URL '': seems to be because of failure to run post action for actions/setup-pages
• set-output deprecated; use environment files; all from actions/setup-pages

Broken:

• Poetry installer; migrate to the abatilo/actions-poetry@v2 action

Best practice:

• Split the build and deploy jobs; it's easier to understand what's going on and easier to configure checks against in rulesets