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/models/form/account_batch.rb

@@ -103,7 +103,7 @@ class Form::AccountBatch
     authorize(account.user, :reject?)
     log_action(:reject, account.user, username: account.username)
     account.suspend!(origin: :local)
-    AccountDeletionWorker.perform_async(account.id, reserve_username: false)
+    AccountDeletionWorker.perform_async(account.id, { 'reserve_username' => false })
   end
 
   def suspend_account(account)