[BUG] Generate Java code with multiple enum values using allOf

Description

When generating the Java code with allOf and each item has a different value for the same enum, the multiples values are not combined in the result class.

openapi-generator version

openapi-generator-maven-plugin: 7.10.0

OpenAPI declaration file

openapi: "3.0.3"
info:
  title: "Test enum"
  version: "1.0.0"
paths:
  /api/test:
    post:
      requestBody:
        content:
          pet:
            schema:
              $ref: "#/components/schemas/Pet"
      responses:
        "201":
          description: "Created"
          content:
            pet:
              schema:
                $ref: "#components/schemas/Pet        "
components:
  schemas:
    Pet:
      allOf:
        - $ref: "#/components/schemas/Cat"
        - $ref: "#/components/schemas/Dog"
      type: "object"
    Dog:
      type: "object"
      additionalProperties: false
      properties:
        'type':
          type: "string"
          enum:
            - "Dog"
        age:
          type: "string"
    Cat:
      type: "object"
      additionalProperties: false
      properties:
        'type':
          type: "string"
          enum:
            - "Cat"
        name:
          type: "string"

Generation Details

Java Maven plugin configuration:

<plugin>
    <groupId>org.openapitools</groupId>
    <artifactId>openapi-generator-maven-plugin</artifactId>
    <version>7.10.0</version>
    <configuration>
        <skipIfSpecIsUnchanged>true</skipIfSpecIsUnchanged>
        <generatorName>spring</generatorName>
        <configOptions>
            <dateLibrary>java8</dateLibrary>
            <oas3>true</oas3>
            <annotationLibrary>none</annotationLibrary>
            <documentationProvider>none</documentationProvider>
            <containerDefaultToNull>true</containerDefaultToNull>
        </configOptions>
    </configuration>
</plugin>

Steps to reproduce

Just build the project.

Suggest a fix

The Pet class should be generated with the enum 'type' having the values Cat and Dog, but the Pet class has only one value for the enum Type.

Reproduce the issue with the provided OpenAPI declaration and the openapi-generator-maven-plugin using the Spring generator. Inspect the generated Pet class and the handling of the shared type enum across the Cat and Dog allOf references. Done means the generated enum contains both Cat and Dog values and the regression is covered by an appropriate generator test.