select() re-selects once deferred single-use-token refreshes complete;
acquire_lease() performed the refresh but returned its pre-refresh
answer. Since _acquire_lease_under_lock returns early exactly when a
refresh is pending (if not available: return None, pending_refresh),
a pool whose entries all needed a refresh always returned None — the
caller failed an answerable request right after the refresh succeeded.
Retry once, only when the first pass was empty and a refresh ran.
Post-merge gate-sweep finding on the #71775 salvage (#77714).
kshitijk4poor