[kotlin-client] Fix string comparison in discriminator post-processing (#21881)

We encountered occassional build failures with the logic introduced in #21531 due to discriminator properties still being generated in rare cases.
Not sure why it didn't happen consistently, may be related to Gradle caching or parallel builds or whatever.
Since patching these string comparisons, this has no longer occurred.

Author: Gama11

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

@@ -976,7 +976,7 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
                         continue;
                     }
                     // Remove discriminator property from the base class, it is not needed in the generated code
-                    getAllVarProperties(cm).forEach(list -> list.removeIf(var -> var.name == discriminator.getPropertyName()));
+                    getAllVarProperties(cm).forEach(list -> list.removeIf(var -> var.name.equals(discriminator.getPropertyName())));
 
                     for (CodegenDiscriminator.MappedModel mappedModel : discriminator.getMappedModels()) {
                         // Add the mapping name to additionalProperties.disciminatorValue
@@ -989,7 +989,7 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
                         }
                         additionalProperties.discriminatorValue = mappedModel.getMappingName();
                         // Remove the discriminator property from the derived class, it is not needed in the generated code
-                        getAllVarProperties(mappedModel.getModel()).forEach(list -> list.removeIf(prop -> prop.name == discriminator.getPropertyName()));
+                        getAllVarProperties(mappedModel.getModel()).forEach(list -> list.removeIf(prop -> prop.name.equals(discriminator.getPropertyName())));
                     }
 
                 }