[BUG][typescript-fetch] implicit any in runtime.ts

Created by: Teyras

Description

The querystring function defined in https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache#L186 has an implicit return type of any. This is a problem when using the generated client with create-react-app.

openapi-generator version

4.0.0-SNAPSHOT from dockerhub