Fix instance level after_unlock callback (#737)

BACKGROUND -------------------------------------------------------------

#707 introduced a regression where the instance level `after_unlock`
callback is no longer being called. This was due to the change of using
`item[CLASS]` instead of `worker_class` to set `job_class` in
`SidekiqUniqueJobs::Middelware#call`. `item[CLASS]` is a string, where
as `worker_class` can be either an instance, or the class itself. For the
instance level `after_unlock` to work, we need `job_class` to be an
instance of the worker.

This fixes the issue by switching back to setting `job_class` to
`worker_class`

CHANGELOG --------------------------------------------------------------

- Use worker_class for self.job_class in Middleware#call

Co-authored-by: Mikael Henriksson <[email protected]>

lib/sidekiq_unique_jobs/middleware.rb

@@ -32,7 +32,7 @@ def call(worker_class, item, queue, redis_pool = nil)
       @item       = item
       @queue      = queue
       @redis_pool = redis_pool
-      self.job_class = item[CLASS]
+      self.job_class = worker_class
       return yield if unique_disabled?
 
       SidekiqUniqueJobs::Job.prepare(item) unless item[LOCK_DIGEST]