Fix TypeError: 'PosixPath' object is not iterable

[glenn-jocher]

Fix for error produced when evolving:

Traceback (most recent call last):
  File "train.py", line 617, in <module>
    results = train(hyp.copy(), opt, device)
  File "train.py", line 422, in train
    for m in (last, best) if best.exists() else (last):  # speed, mAP tests
TypeError: 'PosixPath' object is not iterable

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improved consistency in test model selection logic in training script.

📊 Key Changes

• Adjusted the tuple to a list when determining which models (last, best) to test after training.

🎯 Purpose & Impact

• The change ensures consistent behavior in the selection of models for testing, leading to more reliable post-training evaluations.
• Users can expect consistent testing of both the last and best models when they exist, without any unintended logic errors.