* 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.
