Fix sort_by failing if a tag does not exist in TAG_ORDER

[Skipants]

Fixes an error if another tag is added to a model parsed by SwaggerYard eg. YARD::Tags::Library.define_tag('MuCustomTag', :my_custom_tag)

We have custom tags on our models that would cause warning messages when hit by ::Yard.parse. To suppress these warning messages, we define these custom tags in yard like so:

YARD::Tags::Library.define_tag('Custom Tag', :custom_tag)

In doing so, however, it causes spec = SwaggerYard::OpenAPI.new.to_h to error out at the line changed in this PR since the custom tag does not exist in TAG_ORDER.

Since the case statement following the fixed line is a no-op on custom tags we can simply set the sort value of those tags to 0 to avoid nil comparisons and keep them in the sorted_tags array.

Command run (our custom rake task to generate OpenAPI docs):
time bundle exec rails swagger_yard:generate --trace

Error:

rails aborted! ArgumentError: comparison of Array with Array failed /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/model.rb:48:in `sort_by' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/model.rb:48:in `parse_tags' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/model.rb:14:in `block in from_yard_object' <internal:kernel>:90:in `tap' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/model.rb:12:in `from_yard_object' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:47:in `block (3 levels) in parse_models' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:46:in `map' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:46:in `block (2 levels) in parse_models' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:45:in `map' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:45:in `block in parse_models' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:44:in `map' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:44:in `parse_models' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:36:in `models' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/specification.rb:26:in `model_objects' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/openapi.rb:29:in `components' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/openapi.rb:23:in `definitions' /Users/andrewszczepanski/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/swagger_yard-1.1.1/lib/swagger_yard/openapi.rb:4:in `to_h' /Users/andrewszczepanski/code/platform-core/lib/tasks/swagger_yard.rake:13:in `block (2 levels) in <main>' 

This duplicates #81 because I needed to change the downstream branch.