Disable Rails' deprecated to_s override

This option was deprecated in Rails 7.0 and removed in Rails 7.1 [1]. It
doesn't really affect us because we weren't using `to_s` with a
parameter anywhere in the application.

The Rubocop rule Rails/ToSWithArgument can be used to detect these cases
but, since we've never used them, and adding them now would cause the
application to crash and so it'll be obvious we've done something wrong,
I don't think it's necessary to add the rule.

[1] https://github.com/rails/rails/commit/e420c3380

config/application.rb

@@ -30,6 +30,10 @@ module Consul
     # and you have no plans to rollback.
     config.active_support.cache_format_version = 7.0
 
+    # Disables the deprecated #to_s override in some Ruby core classes
+    # See https://guides.rubyonrails.org/configuring.html#config-active-support-disable-to-s-conversion for more information.
+    config.active_support.disable_to_s_conversion = true
+
     # Keep belongs_to fields optional by default, because that's the way
     # Rails 4 models worked
     config.active_record.belongs_to_required_by_default = false