Add eval mode after loading saved model

[shivansh45334]

Description

Add model.eval() after loading a saved model in the Save and Load Model tutorial.

This ensures the loaded model is explicitly switched to evaluation mode before inference.

Related Issue

Closes #3965

Testing

• Verified the modified Python file with py_compile.
• Tested loading a saved PyTorch model and calling model.eval().
• Verified the model's training attribute is False.
• Ran git diff --check with no errors.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/tutorials/3967

• 📄 Preview Python docs built from this PR

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