Quarantine flaky tests for Run Pipeline form

What does this MR do and why?

See #375552 (closed). The tests are flaky and some additional time is needed to investigate the issue.

I think this should be safe to quarantine since:

• The frontend feature flag right does nothing at the moment, so the frontend still behaves using REST endpoints for fetching the variables in the Run Pipeline form
• The legacy specs don't seem to be flaky and they still cover some of the tests that are being quarantined

The tests were introduced in !96633 (merged)

Screenshots or screen recordings

How to set up and validate locally

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