The `gossiper::reset_endpoint_state_map` function is supposed to acquire
a lock in order to serialize with `replicate_live_endpoints_on_change`.
The `lock_endpoint_update_semaphore` is called, but its result is a
future - and it is not co_awaited. Therefore, the lock has no effect.
This commit fixes the issue by adding missing co_await.
Fixes: #15361Closes#15362