Fix showing closed issues as open in group/project issues list

What does this MR do and why?

This MR fixes showing closed issues as open in the group/project issues list.

An issue's closedAt property is currently checked to see whether it should display as closed on the issues list. However, we added the closed_at database column 5 years ago and did not backfill the data so issues older than this incorrectly show as open on the issues list. This is fixed by checking the issue's state property instead.

Issue: #356815 (closed)

Behind feature flag vue_issues_list defaulted to off.

Screenshots or screen recordings

No visual changes

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:vue_issues_list)

2. Visit any group or project issue list page such as http://127.0.0.1:3000/h5bp/html5-boilerplate/-/issues/
3. Check that closed issues are shown as closed

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.