[QUARANTINE] Plan Assign Iterations assigns a group iteration to an existing issue

What does this MR do?

Quarantines the test Plan Assign Iterations assigns a group iteration to an existing issue (https://gitlab.com/gitlab-org/gitlab/-/blob/master/qa/qa/specs/features/ee/browser_ui/2_plan/iterations/assign_group_iteration_spec.rb#L50)

This test has been found by Confiner to have failed 3 times, which meets the threshold of 3 times.

1. e2e:package-and-test-results
2. e2e:package-and-test-results
3. e2e:package-and-test-results

#376070 (closed)

(This MR was automatically generated by Confiner at 2022-10-01 01:58:01 UTC)