[Low priority] Rails deprecation warning during CI runs

[larouxn]

Looks like there's a bit of cleanup that can be done re: Rails configuration, as the following deprecation warning appears in CI.

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 <top (required)> at /Users/larouxn/src/github.com/activemerchant/payment_icons/test/dummy/config/environment.rb:3)
Run options: --seed 38411