Handle case of two users submitting a WPT coverage evaluation at the same time #5760
Description
Outside the scope of this PR, but it made me think about the scenario where two people try to try/retry at roughly the same time. I wonder if there's a small chance of a race condition where the pipeline could be triggered twice. It might be worth investigating if adding @ndb.transactional to the do_post method would be a good safeguard here. Just a thought for the future!