Update export.py to tensorflow<=2.15.1

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced TensorFlow compatibility in YOLOv5 export functionality.

📊 Key Changes

• Modified how TensorFlow requirements are checked in export.py.
• Specific version constraint added for TensorFlow: <=2.15.1.

🎯 Purpose & Impact

• Purpose: This change aims to ensure compatibility and stability by limiting the TensorFlow version used during the export process. It specifically targets the scenario where the environment might have an incompatible version of TensorFlow installed.
• Impact: Users can expect more reliable exports of YOLOv5 models to TensorFlow formats, with reduced chances of encountering version-related issues. This enhances the overall usability and user experience, especially for those working in environments with specific TensorFlow version requirements. It's particularly useful for developers and researchers looking to deploy YOLOv5 models in TensorFlow-supported platforms. 🚀