[BUG] Generated cpp-qt-client contains errors

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

Client's code generated with docker
docker run --rm -v $PWD:/local openapitools/openapi-generator-cli:latest generate -i /local/vmd-api/openapi.yaml -g cpp-qt-client -o /local/openapi-client-code
has errors:
error: ‘const class QJsonValue’ has no member named ‘isSet’
error: ‘const class QJsonValue’ has no member named ‘asJsonObject’
According to qt spec there is no such methods as isSet() and asJsonObject() which present in the generated client code.

openapi-generator version

I tried 5.4.0, 6.5.0 and the latest as proposed here.

https://github.com/tiiuae/vmd/blob/main/vmd-api/openapi.yaml

Reproduce the issue with the provided Docker command, the cpp-qt-client generator, and vmd-api/openapi.yaml. Inspect the generated client where QJsonValue is used and compare isSet() and asJsonObject() with the Qt API. Done means the generated client compiles without these errors.