swagger-codegen 3.0.71 generates illegal code for Java 21

[JuergenSimon]

I am trying to generate a client for the paperlessngx REST API, which is openapi: 3.0.3.

The API has some enums, like this:

        name: type
        schema:
          type: string
          title: Task Type
          enum:
          - auto_task
          - manual_task
          - scheduled_task
        description: |-
          The type of task that was run

This winds up with a compilation error in Java:

XXX/src/rasff-sws/target/generated-sources/swagger/src/main/java/io/swagger/client/model/AllOfTasksViewRequestType.java:25:48 java: cannot inherit from final io.swagger.client.model.TasksViewTypeEnum

This makes perfect sense, as AllOfTasksViewRequestType.java looks like this:

public class AllOfTasksViewRequestType extends TasksViewTypeEnum {

  @Override
  public boolean equals(java.lang.Object o) {

I have no idea how this code is supposed to compile. Was this construct legal in Java 11? At any rate, we must use Java 21 and how do I fix this problem?