[E2E] PROMOTE TO BLOCKING: gitlab_migration_issue_spec.rb

What does this MR do?

Promotes the following e2e tests to the blocking bucket:

1. Manage Gitlab migration with designs successfully imports design | Testcase | Spec metrics

2. Manage Gitlab migration with associated merge request preserves related merge request | Testcase | Spec metrics

This MR was created based on data from reliable e2e test report: #505956

(This MR was automatically generated by gitlab_quality-test_tooling at 2024-11-25 02:05:35 UTC)