Use until_executed for CI sync workers

What does this MR do and why?

This MR uses the until_executed deduplication strategy for the project and namespace sync workers. The goal here is to reduce the number of parallel sync jobs.

Suggested by reprazent via slack: https://gitlab.slack.com/archives/C01TQ838Y3T/p1647854968654609?thread_ts=1647825450.117729&cid=C01TQ838Y3T

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.