Simplify container CI

[johnthagen]

• Condense container job into a single CI job
• The docker/build-push-action does not require the Git checkout step
  • https://github.com/docker/build-push-action?tab=readme-ov-file#git-context

By default, this action uses the Git context, so you don't need to use the actions/checkout action to check out the repository as this will be done directly by BuildKit.