feat: Include requirements files in cache

[henrikwidlund]

Description

• Always use cache in setup-python
• Include dependency files in cache
• Specify versions in test-requirements.txt to avoid stale caches

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Not testable, will be tested in CI.

Checklist:

• My code follows the code guidelines of this project
• My pull request represents one logical piece of work. Do not combine multiple unrelated changes into a single pull request.
• My changes pass the linter checks (see code guidelines) and unit tests python -m unittest discover tests. PRs with failing linter or unit tests will not be merged.
• I have tested and performed a self-review of my code