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/services/import_service.rb

@@ -76,7 +76,7 @@ class ImportService < BaseService
         if presence_hash[target_account.acct]
           items.delete(target_account.acct)
           extra = presence_hash[target_account.acct][1]
-          Import::RelationshipWorker.perform_async(@account.id, target_account.acct, action, extra)
+          Import::RelationshipWorker.perform_async(@account.id, target_account.acct, action, extra.stringify_keys)
         else
           Import::RelationshipWorker.perform_async(@account.id, target_account.acct, undo_action)
         end
@@ -87,7 +87,7 @@ class ImportService < BaseService
     tail_items = items - head_items
 
     Import::RelationshipWorker.push_bulk(head_items + tail_items) do |acct, extra|
-      [@account.id, acct, action, extra]
+      [@account.id, acct, action, extra.stringify_keys]
     end
   end