Add tests for oneOf models in ruby client (#16137)

* add test for oneOf model in ruby

* add new files

* add tests for oneOf model without discriminator

Author: wing328

bin/configs/ruby.yaml

@@ -1,7 +1,7 @@
 generatorName: ruby
 outputDir: samples/client/petstore/ruby
 library: typhoeus
-inputSpec: modules/openapi-generator/src/test/resources/3_0/petstore-with-fake-endpoints-models-for-testing.yaml
+inputSpec: modules/openapi-generator/src/test/resources/3_0/ruby/petstore-with-fake-endpoints-models-for-testing.yaml
 templateDir: modules/openapi-generator/src/main/resources/ruby-client
 additionalProperties:
   gemVersion: 1.0.0