github: Use setup-python and setup-poetry for system tests

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

Update run_system_tests.yml to use ni/python-actions/setup-python and ni/python-actions/setup-poetry.

Why should this Pull Request be merged?

Allow ni/python-actions to specify the default Python and Poetry versions used to run Tox.

What testing has been done?

PR build

[github-actions]

Test Results

    38 files  ±0      38 suites  ±0   1h 3m 5s ⏱️ +54s
 2 835 tests ±0   2 243 ✅ ±0    592 💤 ±0  0 ❌ ±0 
48 968 runs  ±0  40 280 ✅ ±0  8 688 💤 ±0  0 ❌ ±0 

Results for commit c6bc759. ± Comparison against base commit d629c76.

♻️ This comment has been updated with latest results.

[bkeryan]

FYI, we will also want this ni/python-actions change: ni/python-actions#26

This changes the Poetry install directory and includes this directory in the cache key. The old Poetry install directory was in $HOME, and this is a different directory between GitHub-hosted and self-hosted runners.

[zhindes]

🎉