[BUG] [Kotlin] Generated api client doesn't work for plain text response body types

[Yonggo]

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• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
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Description

openapi-generator version

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

accept content type is not set in the generated client code unless application/json is used as response tpye:

therefore it come always error "HttpMediaTypeNotAcceptableException" during integrationtest

[ffffionn]

This is a big deal I think, the "text/plain" media type should be supported

[0sten]

Issue is still present when client is ktor.