Stringify on_conflict hash in Job prepare method

[jasonbekolay]

Unfortunately my PR yesterday did not resolve the issue. While we did correct worker_options, it turns out that in the client it doesn't follow that code path when there's a conflict. My apologies for missing the mark, I didn't test thoroughly enough.

I was able to determine the root cause of the issue. The job_hash is stringified by Sidekiq.default_worker_options, and it's just a shallow stringify. That means the on_conflict hash still has symbols for keys by the time it gets to find_strategy.

The approach I took to resolve is to stringify the hash in Job#prepare. I'm happy to change or tweak the approach on your advice.

Thanks for your time recently and the quick release! Hopefully this change fixes this issue for good.

[mhenrixon]

Released as v7.0.0.beta18!

[jasonbekolay]

Thanks for the quick attention and release! Currently running in production and it looks good so far!