HYBIM 795 | Fix poetry cache invalidation

[keith-decker]

Summary

Fixes HYBIM-795 by preserving the Poetry cache restored by actions/setup-python in the main CI test workflow.

What changed

• Added id: setup-python to the matrix Python setup step.
• Replaced the destructive poetry env remove --all flow with:

  poetry env use "${{ steps.setup-python.outputs.python-path }}"
  

• Kept the pre-install and post-install Poetry Python version checks to ensure each matrix job still uses the requested Python version.

Validation

• git -C splunk-ao-python diff --check
• Confirmed poetry env remove --all is no longer present in .github/workflows/ci-tests.yaml
• Confirmed Poetry uses steps.setup-python.outputs.python-path
• Confirmed both interpreter checks remain present before and after dependency installation

Not run

• GitHub Actions cold-cache / warm-cache validation was not run or inspected locally.