This prevents someone from setting `config.seed` in an `RSpec.configure` block or even from within RSpec (I think when the seed is forced, it is set after `lock_seed` is called), but now it gets used since it is passed in to `lock_seed` and that parameter takes priority.

Regardless of anything, I think the seed should be locked down as soon as it is actually used for seeding randomization. I don't see any reason we should allow it to be changed after that.