use elixir petstore spec for testing (#20236)

Author: wing328

bin/configs/elixir.yaml

@@ -1,6 +1,6 @@
 generatorName: elixir
 outputDir: samples/client/petstore/elixir
-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/elixir/petstore-with-fake-endpoints-models-for-testing.yaml
 templateDir: modules/openapi-generator/src/main/resources/elixir
 additionalProperties:
   invokerPackage: OpenapiPetstore