81d50bde33
Stamp `orphaned_at = now()` on the ref-0 row so it sits inside the
GC grace window for the duration of this test. Without it,
`orphaned_at IS NULL` is treated by `garbage_collect` as
"pre-migration, immediately reapable" — and any sibling test in
the shared pool that calls `garbage_collect()` (e.g.
`garbage_collect_respects_grace_and_cross_checks`) would race
with the pin below and delete the row first.