Bump actions/checkout from v6 to v7 in /.github/workflows

[UltralyticsAssistant]

Bump actions/checkout from v6 to v7 in /.github/workflows

This PR updates GitHub Actions references in this repository.

Examples:

• Branch: actions/checkout@main stays on @main
• Major tag: actions/checkout@v4 updates to @v5
• Specific tag: astral-sh/setup-uv@v0.5.0 updates to @v0.9.4
• SHA pinned: actions/checkout@<sha> # v4.1.0 updates to the latest release SHA and tag comment

_{Made with ❤️ by Ultralytics Actions}

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

🔧 This PR updates the GitHub Actions checkout step from actions/checkout@v6 to actions/checkout@v7 in the repository’s CI and push workflows.

📊 Key Changes

• Updated .github/workflows/ci.yml to use actions/checkout@v7 instead of @v6.
• Updated .github/workflows/push.yml to use actions/checkout@v7 instead of @v6.
• No model logic, training code, or inference behavior was changed—this is a workflow maintenance update only. 🛠️

🎯 Purpose & Impact

• Keeps the repository’s GitHub Actions workflows up to date with the latest supported checkout action. ✅
• Helps improve long-term reliability, compatibility, and maintainability of automated CI and push processes. 🔄
• Reduces the risk of using outdated workflow dependencies, with little to no impact on end users or model behavior. 📦