[E2E] PROMOTE TO BLOCKING: register_group_runner_spec.rb

What does this MR do?

Promotes the following e2e tests to the blocking bucket:

1. Verify Group runner registration user registers a new group runner | Testcase | Spec metrics

This MR was created based on data from reliable e2e test report: #468109 (closed)

(This MR was automatically generated by gitlab_quality-test_tooling at 2024-06-19 06:08:42 UTC)