Remove blocked status on issues when blocking issue is closed

Summary

Blocked issues on boards retain their blocked icon even when blocking issues are fully closed.

Steps to reproduce

1. Go to an issue board
2. In one of the open columns mark an issue as blocked by another open issue
3. Close the blocking issue
4. Observe the closed issue in the closed column but blocked issue still marked as blocked.

Example Project

Best use gdk to reproduce

What is the current bug behavior?

Backend returns blocked: true for an issue that is blocked only by closed issues.

What is the expected correct behavior?

Backend should return blocked: false for issues that have no open blocking issues.

Possible fixes

We may want to use the relationship with closed blocking issues in other parts of the application (e.g. to see historical blockages/pathways to completion, or to show blocking issues as closed in the 'related issues' box) so we should probably use a select in the EE::Boards::IssuesController https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/controllers/ee/boards/issues_controller.rb#L10 to filter exclusively for boards.