scala-sttp4: fix for missing EnumNameSerializer for inner enum definitions (#18145) (#18160)

Author: dwischolek-modulon

modules/openapi-generator/src/main/resources/scala-sttp4/jsonSupport.mustache

@@ -11,7 +11,8 @@ import scala.reflect.ClassTag
 
 object JsonSupport extends SttpJson4sApi {
   def enumSerializers: Seq[Serializer[_]] = Seq[Serializer[_]](){{#models}}{{#model}}{{#isEnum}} :+
-    new EnumNameSerializer({{classname}}){{/isEnum}}{{/model}}{{/models}}
+    new EnumNameSerializer({{classname}}){{/isEnum}}{{#hasEnums}}{{#vars}}{{#isEnum}} :+
+    new EnumNameSerializer({{classname}}Enums.{{datatypeWithEnum}}){{/isEnum}}{{/vars}}{{/hasEnums}}{{/model}}{{/models}}
 
   private class EnumNameSerializer[E <: Enumeration: ClassTag](enumeration: E) extends Serializer[E#Value] {
     import JsonDSL._

samples/client/petstore/scala-sttp4/src/main/scala/org/openapitools/client/core/JsonSupport.scala

@@ -17,7 +17,9 @@ import sttp.client4.json4s.SttpJson4sApi
 import scala.reflect.ClassTag
 
 object JsonSupport extends SttpJson4sApi {
-  def enumSerializers: Seq[Serializer[_]] = Seq[Serializer[_]]()
+  def enumSerializers: Seq[Serializer[_]] = Seq[Serializer[_]]() :+
+    new EnumNameSerializer(OrderEnums.Status) :+
+    new EnumNameSerializer(PetEnums.Status)
 
   private class EnumNameSerializer[E <: Enumeration: ClassTag](enumeration: E) extends Serializer[E#Value] {
     import JsonDSL._