Update _make_grid() to model dtype

[glenn-jocher]

Per #6268 (comment)

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improved tensor type consistency in YOLO grid creation.

📊 Key Changes

• Ensured the tensors for creating grids match the data type of the associated anchors.
• Modified the _make_grid function for better compatibility and efficiency.

🎯 Purpose & Impact

• 🎯 Purpose: To maintain data type consistency throughout the model, which can prevent potential errors and ensure more predictable behavior.
• 💡 Impact: Users may experience increased robustness and possibly a slight performance improvement during model training or inference, as well as better compatibility with different versions of PyTorch.