[QUARANTINE] Plan Epics milestone dates API updates epic dates when adding another issue

What does this MR do?

Quarantines the test Plan Epics milestone dates API updates epic dates when adding another issue (https://gitlab.com/gitlab-org/gitlab/-/blob/master/qa/qa/specs/features/ee/api/2_plan/epics_milestone_dates_spec.rb#L46)

This test has been found by Confiner to have been failing for more than (or equal to) 3 times. This test has failed 4 times.

1. ee:instance-parallel
2. ee:relative_url-parallel
3. ee:update-parallel
4. ee:praefect-parallel

#335632 (closed)

(This MR was automatically generated by Confiner at 2022-01-21 01:58:52 UTC)