[prototype runtime] Fix error if direct inherited

[ksss]

rbs: 3.3.0.pre.1

When trying to analyze the faraday gem using rbs prototype runtime, an error occurs.
This is due to StructGenerator not considering patterns like class Option < Struct.
In this case, I made a modification to exclude it from the generator target.

repro

$ bundle exec rbs prototype runtime -r faraday Faraday::Options

before

bundler: failed to load command: rbs (/bundle/ruby/3.2.0/bin/rbs)
/bundle/ruby/3.2.0/gems/rbs-3.3.0.pre.1/lib/rbs/prototype/runtime/value_object_generator.rb:107:in `block in build_s_new': undefined method `keyword_init?' for Faraday::Options:Class (NoMethodError)

            if CAN_CALL_KEYWORD_INIT_P ? (@target_class.keyword_init? == false || @target_class.keyword_init? == nil) : true
                                                       ^^^^^^^^^^^^^^

after

module Faraday
  class Options < ::Struct[untyped]
  end
end

[soutaro]

Thanks! 👍