#71775 moved deferred single-use-token refreshes outside the pool lock
(correct — they hold a cross-process flock plus network I/O). But
_refresh_entry_impl's three terminal-auth-failure quarantine paths do a
bare read-modify-write of self._entries. Those used to run with the
caller holding self._lock; on the deferred path they run unlocked, so a
concurrent mutation between the read and the write is silently lost.
Wrap all three in 'with self._lock' (an RLock, so locked callers
re-enter safely) and correct the _refresh_pending_entries docstring,
which claimed the mutations were already self-locking.
Post-merge gate-sweep finding on the #71775 salvage (#77714).
Sibling to the acquire_lease re-select fix.
kshitijk4poor