fix double serialization (#22924)

Author: dschodits-secunet

modules/openapi-generator/src/main/resources/Java/typeInfoAnnotation.mustache

@@ -4,8 +4,12 @@
 @JsonIgnoreProperties(
   value = "{{{discriminator.propertyBaseName}}}", // ignore manually set {{{discriminator.propertyBaseName}}}, it will be automatically generated by Jackson during serialization
   allowSetters = true // allows the {{{discriminator.propertyBaseName}}} to be set during deserialization
-){{/disableDiscriminatorJsonIgnoreProperties}}
+)
 @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
+{{/disableDiscriminatorJsonIgnoreProperties}}
+{{#disableDiscriminatorJsonIgnoreProperties}}
+@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
+{{/disableDiscriminatorJsonIgnoreProperties}}
 {{#discriminator.mappedModels}}
 {{#-first}}
 @JsonSubTypes({