VLN-1608: remediate checkout-below-v7

[picatz]

🏕️ This pull request was created by camper, an automated security campaign tool.

Finding

Rule	checkout-below-v7
Severity	MEDIUM
Repository	temporalio/samples-ruby
Ticket	VLN-1608

Summary

• .github/workflows/ci.yml: Updated the actions/checkout step to the required v7.0.0 commit pin.

Instructions

• Approve to merge this fix
• Request changes to trigger a new remediation attempt
• /camper rebase — rebase onto the base branch
• /camper close — close this PR without merging
• /camper retry — regenerate the fix from scratch against the current base

[picatz]

This PR has had no activity for 9 days and may need attention.

Actions you can take:

• Review and approve if the changes look good
• Close if this fix is no longer needed
• Comment /camper rebase to rebase onto the latest base branch
• Comment /camper retry to regenerate the fix

[picatz]

This PR has had no activity for 7 days and may need attention.

Actions you can take:

• Review and approve if the changes look good
• Close if this fix is no longer needed
• Comment /camper rebase to rebase onto the latest base branch
• Comment /camper retry to regenerate the fix