Disallow --dynamic when --half is passed

[dmatos2012]

Hi,
Add this assertion when dynamic is given as well as the --half argument to avoid the error as mentioned in issue #7641.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced compatibility checks in YOLOv5 model export script.

📊 Key Changes

• Added a new assertion to export.py that prevents using the --half precision flag in conjunction with the --dynamic flag during model export.

🎯 Purpose & Impact

• Purpose: The update ensures that users do not attempt to export a model with incompatible flags that could lead to errors during the export process.
• Impact: This change improves user experience by providing clear error messages, preventing potential confusion and frustration. It helps maintain the stability and reliability of the model export feature by enforcing correct usage patterns.

[github-actions]

👋 Hello @dmatos2012, thank you for submitting a YOLOv5 🚀 PR! To allow your work to be integrated as seamlessly as possible, we advise you to:

• ✅ Verify your PR is up-to-date with upstream/master. If your PR is behind upstream/master an automatic GitHub Actions merge may be attempted by writing /rebase in a new comment, or by running the following code, replacing 'feature' with the name of your local branch:

git remote add upstream https://github.com/ultralytics/yolov5.git
git fetch upstream
# git checkout feature  # <--- replace 'feature' with local branch name
git merge upstream/master
git push -u origin -f

• ✅ Verify all Continuous Integration (CI) checks are passing.
• ✅ Reduce changes to the absolute minimum required for your bug fix or feature addition. "It is not daily increase but daily decrease, hack away the unessential. The closer to the source, the less wastage there is." -Bruce Lee

[glenn-jocher]

@dmatos2012 PR is merged. Thank you for your contributions to YOLOv5 🚀 and Vision AI ⭐