This is a quick fix for Feature use [RUN ALL RSPEC]

What does this MR do?

Addresses #300104 (closed)

It calls Feature.persist_used! to "fix" that it's not ever being called for real.

After this is merged into master, we'll issue a revert of !52686 (merged) to get back to a state that isn't blocking for new experiments using gitlab-experiment.

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content