[BUG][SPRINGBOOT] The class is generated without extends parent

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

I want to generate a class inheritated from imported external class.
In gradle task im using importMappings to import generated class from another yaml file.
In yaml file im using allOf and $ref to that class.
Class will be generated with import to that class but without of extends keyword.

openapi-generator version

7.11.0

OpenAPI declaration file content or url

https://gist.github.com/p-migda/c32e0e2623024a00cd068343cc6c25d2
https://gist.github.com/p-migda/f9c211cfb5849cd3cc32841b3d0f63b4

Generation Details

using openapi-generator-gradle-plugin:

tasks.register('generateParent', GenerateTask) {
    skipOperationExample = true
    generatorName = 'spring'
    inputSpec = "$projectDir/exampleParent.yaml"
    outputDir = "$projectDir"
    apiPackage = 'org.example.document.generated.api'
    modelPackage = 'org.example.document.generated.model'
    configOptions = [
            'useSpringBoot3'                : 'true',
            'interfaceOnly'                 : 'true',
            'serializationLibrary'          : 'jackson',
            'dateLibrary'                   : 'java8',
            'library'                       : 'spring-boot',
            'sourceFolder'                  : targetFolder,
            'bigDecimalAsString'            : 'false',
            'additionalModelTypeAnnotations': ';@com.fasterxml.jackson.annotation.JsonInclude(' +
                    'com.fasterxml.jackson.annotation.JsonInclude.Include.NON_NULL);' +
                    '@com.fasterxml.jackson.annotation.JsonIgnoreProperties(ignoreUnknown = true);' +
                    '@lombok.NoArgsConstructor;',
    ]
    additionalProperties = [
            generatedConstructorWithRequiredArgs: 'false'
    ]
}

tasks.register('generateChild', GenerateTask) {
    dependsOn generateParent
    skipOperationExample = true
    generatorName = 'spring'
    inputSpec = "$projectDir/example.yaml"
    outputDir = "$projectDir"
    apiPackage = 'org.example.document.generated.api'
    modelPackage = 'org.example.document.generated.model'
    configOptions = [
            'useSpringBoot3'                : 'true',
            'interfaceOnly'                 : 'true',
            'serializationLibrary'          : 'jackson',
            'dateLibrary'                   : 'java8',
            'library'                       : 'spring-boot',
            'sourceFolder'                  : targetFolder,
            'bigDecimalAsString'            : 'false',
            'additionalModelTypeAnnotations': ';@com.fasterxml.jackson.annotation.JsonInclude(' +
                    'com.fasterxml.jackson.annotation.JsonInclude.Include.NON_NULL);' +
                    '@com.fasterxml.jackson.annotation.JsonIgnoreProperties(ignoreUnknown = true);' +
                    '@lombok.NoArgsConstructor;',
    ]
    additionalProperties = [
            generatedConstructorWithRequiredArgs: 'false'
    ]
    importMappings = [
            'ParentClass': 'org.example.document.generated.model.ParentClass'
    ]
}

Steps to reproduce

Just run a gradleTask

Suggest a fix

Maybe something wrong is with setting a parent marker when parent class is imported from outside of file.

Run the generateParent and generateChild Gradle tasks with the linked exampleParent.yaml and example.yaml specifications. Trace the Spring generator's handling of allOf, $ref, and importMappings when generating the child model. Done means the generated child class imports ParentClass and also extends it when the parent comes from the separately generated specification.