Deprecation warning for `cache_format_version = 6.1` occurring

[larouxn]

Quick heads up that we have this deprecation warning occurring.

DEPRECATION WARNING: Support for `config.active_support.cache_format_version = 6.1` has been deprecated and will be removed in Rails 7.2.

Check the Rails upgrade guide at https://guides.rubyonrails.org/upgrading_ruby_on_rails.html#new-activesupport-cache-serialization-format
for more information on how to upgrade.
 (called from block in <class:App> at /home/larouxn/src/github.com/larouxn/devdocs/lib/app.rb:60)

Looks like we need to update this line, in some way.

https://github.com/freeCodeCamp/devdocs/blob/9a5b70c06613308653970a772123e87b8ec43ede/lib/app.rb#L60