Add Slack message on domain check error

[glenn-jocher]

@kalenmike adds Slack message to Website channel if this daily test fails

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improvements to GitHub Actions workflow with Slack notifications on failure.

📊 Key Changes

• Added a new step in the workflow to send notifications to Slack.
• Notifications are triggered only if the workflow fails during a scheduled run, not if it is manually cancelled.

🎯 Purpose & Impact

• Facilitates Immediate Alerts: The team will receive instant notifications on Slack if the scheduled domain check fails, promoting a quicker response to resolve issues.
• Reduces Noise: By excluding notifications for cancelled runs, the team avoids unnecessary alerts, keeping the focus on genuine problems.