[QUARANTINE] [nightly] Create Download merge request patch and diff views the merge request plain diff

What does this MR do?

Quarantines the test Create Download merge request patch and diff views the merge request plain diff (https://gitlab.com/gitlab-org/gitlab/-/blob/master/qa/qa/specs/features/browser_ui/3_create/merge_request/view_merge_request_diff_patch_spec.rb#L26)

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

1. ee:update
2. ce:upgrade
3. ee:instance-image

#396526 (closed)

(This MR was automatically generated by Confiner at 2023-03-16 01:17:57 UTC)