Update ci-testing.yml

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhancement of CI caching for Python dependencies in the 'ultralytics/yolov5' repository.

📊 Key Changes

• Implemented a new step to determine the cache directory for Python pip dependencies.
• Re-enabled caching for pip in the CI workflow, tuned specifically for different operating systems and Python versions.
• Introduced hashFiles for requirements.txt to create a unique cache key, ensuring relevance of the cache.

🎯 Purpose & Impact

• Faster CI Builds: By restoring dependencies from cache, the time taken for CI builds to complete should decrease significantly.
• Reduced Redundancy: Minimizes repeated work by reusing previously downloaded packages across different CI runs.
• Enhanced Efficiency: Caching dependencies tailored to the operating system and Python version ensure maximum compatibility and efficiency.
• Robust CI Pipelines: Ensures the CI workflow is less prone to network-related issues when fetching dependencies, as they can be sourced directly from the cache.

CI enhancements like this can lead to more rapid integration and testing, speeding up development cycles for contributors and maintainers alike. 🚀