Update ci.yaml for Slack v2

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Upgrade Slack notification action in the GitHub CI workflow to a newer version.

📊 Key Changes

• Updated Slack GitHub Action from version 1.27.0 to 2.0.0.
• Modified configuration to use incoming-webhook for Slack notifications.
• Adjusted how the webhook URL is integrated using the webhook parameter.

🎯 Purpose & Impact

• Enhanced Features: The update to version 2.0.0 provides new features and improved functionality for sending Slack notifications.
• Improved Reliability and Maintenance: By using the incoming webhook method, the integration becomes more reliable and easier to manage.
• Potential Impact: Developers and team members will receive more robust and possibly timely notifications, ensuring they are promptly informed about CI issues, thereby promoting swift resolution and maintaining workflow efficiency. 🚀

[UltralyticsAssistant]

👋 Hello @glenn-jocher, thank you for submitting your PR to the ultralytics/hub repository! 🚀 To ensure a smooth integration process for your updates, please review the following checklist:

• ✅ Define a Purpose: Ensure your PR description clearly delineates the aim of your changes. If applicable, link any relevant issues for additional context. Remember to keep your commit messages clear and concise.
• ✅ Synchronize with Source: Check that your PR is in sync with the main branch of the ultralytics/hub repository. You can update it by clicking 'Update branch' or by using git pull and git merge main locally.
• ✅ Ensure CI Checks Pass: Make sure all Ultralytics Continuous Integration (CI) checks are successful. If any checks fail, please resolve these issues.
• ✅ Update Documentation: Modify or add any necessary content in the documentation to reflect your updates.
• ✅ Add Tests: If applicable, ensure you add or update tests to verify the changes and confirm all tests are passing.
• ✅ Sign the CLA: Verify that you have signed our Contributor License Agreement if this is your first contribution by stating "I have read the CLA Document and I sign the CLA" in a comment.
• ✅ Minimize Changes: Keep your changes as streamlined as possible, focusing on the essential adjustments needed for your feature or bug fix. "It is not daily increase but daily decrease, hack away the unessential." — Bruce Lee.

For more detailed guidance, please check our Contributing Guide. An Ultralytics engineer will review your PR and assist you further shortly. Don't hesitate to leave a comment if you have any questions. Thank you for your valuable contributions to Ultralytics! 🌟