Add json as an explicit dependency

[deivid-rodriguez]

Description

This is similar to #1573, but for json.

In this case, I'm not getting a warning about json but about ostruct, i.e., it's not json that's being removed as a default gem in Ruby 3.5, but ostruct:

/home/deivid/.asdf/installs/ruby/3.3.5/lib/ruby/3.3.0/json/common.rb:3: warning: ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.

You can add ostruct to your Gemfile or gemspec to silence this warning.

ostruct is getting loaded by json though, and json is getting loaded by faraday.

json has fixed the problem by autoloading the class that uses ostruct at ruby/json@b507f9e. However, I can't really pick up the fix, since json is not a explicit dependency of faraday, so the default version of it always get loaded.

So the only thing remaining to fix the issue would be for faraday to declare its dependency on json. That way, Bundler will be aware of the dependency and a bundle update json can be used to pick up a json version that does not load ostruct and thus avoid the warning.

[olleolleolle]

Thanks, @deivid-rodriguez!