Retry QA runner fabrication

What does this MR do and why?

In #409089 (comment 1385500447), it was discovered that delays occur when QA runners are fabricated leading to QA failures anytime the Namespace#schedule_sync_event_worker sidekiq queue gets backed up.

This MR wraps the failing GET request in a retry, allowing up to 3 retries.

This is related to incident gitlab-com/gl-infra/production#13919 (closed).

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