Add Slack notification of CI errors

[glenn-jocher]

🤖 Generated by Copilot at 1e88ff9

Summary

🛠️🚀📝

Improved link checker workflow by excluding a testing file. This file contains invalid links that are used to test the link checker tool itself, and should not affect the workflow status.

To check links, we use a handy tool
But it flagged a file meant for testing, how cruel
So we added an argument
To exclude it from the judgment
And now the link checker workflow is cool

Walkthrough

• Exclude ci-testing.yaml from link checking ([link](https://github.com/ultralytics/yolov5/pull/11421/files?diff=unified&w=0#diff-a618bbaa9618d3ffa70846c5371ca23ea8f71f3370d3aa5be5d2cf39b42b207bL26-R26), [link](https://github.com/ultralytics/yolov5/pull/11421/files?diff=unified&w=0#diff-a618bbaa9618d3ffa70846c5371ca23ea8f71f3370d3aa5be5d2cf39b42b207bL36-R36))

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improvements in CI notifications and link-checking within Ultralytics YOLOv5 workflows.

📊 Key Changes

• Added a Slack notification step to Continuous Integration (CI) testing, triggered on failures for scheduled or push events.
• Updated the link-checker configuration to exclude the ci-testing.yml file, ensuring that checks are more targeted and relevant.

🎯 Purpose & Impact

• 🔔 Enhanced Communication: The Slack notification provides real-time alerts on CI failures, allowing for swift action and ensuring continuous code quality.
• 🚫 Reduced Noise: By excluding ci-testing.yml from link checks, unnecessary checks are avoided, improving workflow efficiency and focusing attention on files that impact the user experience.
• 🛠 Improved Maintenance: With these adjustments, maintainers can prioritize critical fixes and contribute to a more stable and reliable software development lifecycle.