[BUG] Qt5 client PetStore example doesn't compile when using openapi 3 specification

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
Have you validated the input using an OpenAPI validator (example)?
What's the version of OpenAPI Generator used?
Have you search for related issues/PRs?
What's the actual output vs expected output?
[Optional] Bounty to sponsor the fix (example)

Description

As explained here, the code generate from the openapi 3 spec of the PetStore example doesn't compile.

openapi-generator version

4.0.3

OpenAPI declaration file content or url

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/3_0/petstore.yaml

Command line used for generation

openapi-generator generate -i petstore.yaml -g cpp-qt5-client

Steps to reproduce

Modify the api specification example in bin/cpp-qt5-petstore.sh to modules/openapi-generator/src/test/resources/3_0/petstore.yaml
Try to compile samples/client/petstore/cpp-qt5/PetStore/PetStore.pro

Related issues/PRs

Run Qt5 client sample test #3415
qt5 client: use openapi 3 spec #3400
Revert "qt5 client: use openapi 3 spec" #3458

Suggest a fix

I find it strange that OAIInline_object* file are generated since they are not used anywhere...