Flaky: ployz-store Postgres partition (store-1) failed once in merge queue, test unknown#3729

The merge-group run for #3726 failed once in rust-tests (store-1), at step "ployz-store tests on Postgres". It stopped after 51 s (run 41299066337, group on main b30c018e7b).

The failure didn't reproduce:

• Locally, the same partition (--partition hash:1/2 --all-features, Postgres 16, fsync off) passed 626/626 on the rebased head, which includes #3723.
• PR CI on the rebased head abd3948b0d passed store-1 and store-2 on both Postgres and SQLite (run 41302363370).

The failing test can't be named: the job log blob isn't retrievable, and the uploaded artifact only holds build timings. If it recurs, capture the nextest output. It may also be worth making the store jobs keep their failure output as an artifact.