[BUG] cpp-restsdk inheritance of classes is not written into .h file

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?
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Description

When having inheritance from another class cpp-restsdk generator does not generate the correct .h file for the derived class.
The declaration of the superclass is missing.

What is generated:
class ChildClass : public ModelBase { ... }

What I would expect:
class ChildClass : public ModelBase, public SuperClass { ... }

hint: #include for the SuperClass is generated as expected

openapi-generator version

openapi-generator-maven-plugin v6.6.0

OpenAPI declaration file content or url

Generation Details

generated with openapi-generator-maven-plugin

Steps to reproduce

Related issues/PRs

Suggest a fix

Start by reproducing the supplied SuperClass and ChildClass OpenAPI schemas with openapi-generator-maven-plugin v6.6.0 and inspect the generated cpp-restsdk header. Compare the derived class declaration with the expected inheritance list, while checking that the SuperClass include remains present. Done means the generated .h file declares both ModelBase and SuperClass as base classes.