Fix return value of base_lock

When using the `on_conflict` `replace` strategy `base_lock` has to
return the return value of the conflict strategy. The replace strategy
removes the previous job from the scheduled/rety set or the queue.
It is then re-queued inside `lock_failed`/`call_strategy`, thus we have
to return the return value of which came from `lock` inside the block of
` client_strategy.call`.

lib/sidekiq_unique_jobs/lock/base_lock.rb

@@ -109,7 +109,6 @@ def prepare_item
       def lock_failed(origin: :client)
         reflect(:lock_failed, item)
         call_strategy(origin: origin)
-        nil
       end
 
       def call_strategy(origin:)