Fix Sidekiq warnings about JSON serialization (#17381)

* Fix Sidekiq warnings about JSON serialization

This occurs on every symbol argument we pass, and every symbol key in hashes,
because Sidekiq expects strings instead.

See https://github.com/mperham/sidekiq/pull/5071

We do not need to change how workers parse their arguments because this has
not changed and we were already converting to symbols adequately or using
`with_indifferent_access`.

* Set Sidekiq to raise on unsafe arguments in test mode

In order to more easily catch issues that would produce warnings in production
code.

app/workers/feed_insert_worker.rb

@@ -3,7 +3,7 @@
 class FeedInsertWorker
   include Sidekiq::Worker
 
-  def perform(status_id, id, type = :home, options = {})
+  def perform(status_id, id, type = 'home', options = {})
     @type      = type.to_sym
     @status    = Status.find(status_id)
     @options   = options.symbolize_keys