Use the new method for getting secret_key_base

[jcoyne]

See https://blog.saeloun.com/2023/08/11/rails-7-1-store-secret-key-base-in-rails-config/

[jrochkind]

The gemfile for blacklight main branch allows Rails down to 6.1

blacklight/blacklight.gemspec

Line 28 in a36d8fb

s.add_dependency "rails", '>= 6.1', '< 8'

I don't believe this method is available down that far? You may want to leave the conditional in, but add a branch for Rails.application.respond_to?(:secret_key_base), and maybe drop the one for Rails <= 5.1?

[jcoyne]

@jrochkind it looks like it's present to me: https://github.com/rails/rails/blob/v6.1.7.6/railties/lib/rails/application.rb#L424-L441

[jrochkind]

Oh wacky, thanks for verifying! Why haven't we all been using this API all along, it was clearly right all along, and people were giving bad advice to use other things! Approved