[Ruby] string interpolation in client code dose not work

Description

The interpolation in the error message of Ruby's client dose not work.

Swagger-codegen version

$ java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar version
2.4.2-SNAPSHOT

$ git log --oneline -n 1
c4c5c062c Merge pull request #9080 from swagger-api/update-parser-v1

Swagger declaration file content or url

https://gist.github.com/autopp/5a7375cd9b521b5e5580ba3b1df40c75

The point to notice in this example contains enum in the model.

Command line used for generation

$ java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i 'https://gist.githubusercontent.com/autopp/5a7375cd9b521b5e5580ba3b1df40c75/raw/ca1d5eccce457c7337922b4a6a74f002848e4b4c/swagger.yml' -l ruby -o /tmp/gem

Steps to reproduce

• Run the above command to generate client code for Ruby.
• Generated /tmp/gem/lib/swagger_client/models/x.rb contains string interpolation notation in single-quote string. (It dose not work!)

  def y=(y)
    validator = EnumAttributeValidator.new('String', ["a"])
    unless validator.valid?(y)
      fail ArgumentError, 'invalid value for "y", must be one of #{validator.allowable_values}.'
    end
    @y = y
  end
  

Related issues/PRs

Suggest a fix/enhancement

The corresponding template is this.

I think that it should be a double-quote string.

Start with modules/swagger-codegen/src/main/resources/ruby/partial_model_generic.mustache at the referenced template location. Generate the Ruby client with the provided Swagger declaration and command, then inspect lib/swagger_client/models/x.rb. Done means the generated validation error uses working Ruby string interpolation rather than literal interpolation text.