chore(deps): update actions/checkout action to v6

[dd-octo-sts]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v4 → v6

⚠️ GitHub Actions Major Version Update

This PR updates GitHub Actions dependencies with major version changes. Major updates may include breaking changes.

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• Version Upgrader Overview

• Questions or feedback? Ask in #adms-version-upgrades

🤖 Generated by ADMS (Automated Dependency Management System)

[datadog-datadog-prod-us1]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 57.14% (-0.14%)

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