fix[kotlin]: only use data class when it has constructor vars

[rescribet]

Ran into the issue #14710 as well. The kotlin-spring template is very similar but includes a conditional using #hasVars which controls whether a regular or a data class is generated.

AFAICT that variable comes in somewhere via the CodegenModel since the KotlinSpringServerCodegen doesn't specify it explicitly.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples...
• File the PR against the correct branch: master (upcoming 7.1.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

Comittee members: @jimschubert, @dr4ke616, @karismann, @Zomzog, @andrewemery, @4brunu, @yutaka0m, @stefankoppier

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[wing328]

lgtm, thanks for the PR

have a nice weekend