Update AbstractCSharpCodegen.java (#16577)

Fixed a bug in postProcessAllModels, changing an anyOf to a oneOf.

Author: mol-pensiondk

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java

@@ -527,7 +527,7 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
             // GrandparentAnimal has a discriminator, but no oneOf nor anyOf
             // modules\openapi-generator\src\test\resources\3_0\csharp\petstore-with-fake-endpoints-models-for-testing-with-http-signature.yaml
             model.setHasDiscriminatorWithNonEmptyMapping(
-                    ((model.anyOf != null && model.anyOf.size() > 0) || (model.anyOf != null && model.oneOf.size() > 0)) &&
+                    ((model.anyOf != null && model.anyOf.size() > 0) || (model.oneOf != null && model.oneOf.size() > 0)) &&
                             model.discriminator != null &&
                             model.discriminator.getMappedModels() != null &&
                             model.discriminator.getMappedModels().size() > 0);