[BUG][GO] Add support for all +json and +xml suffixed media types

[joshraker]

Fixes #16811

I don't see tests for the generated client in the repo so I threw together these tests just to sanity-check. They passed ✅.

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[joshraker]

Go Technical Committee: @antihax, @grokify, @kemokemo, @jirikuncar, @ph4r5h4d, @lwj5

[wing328]

thanks for the PR. what about creating a new file named api_cliet_test.go in https://github.com/OpenAPITools/openapi-generator/tree/master/samples/openapi3/client/petstore/go and add some tests for xmlCheck, jsonCheck?

[joshraker]

Thanks for pointing me in the right direction. The members had to be exported in order to test them outside of the package but that shouldn't be a problem. Does https://github.com/OpenAPITools/openapi-generator/tree/master/samples/client/petstore/go need the tests as well?

[wing328]

Does https://github.com/OpenAPITools/openapi-generator/tree/master/samples/client/petstore/go need the tests as well?

No. Eventually we will consolidate the Go petstore tests to use only OpenAPI v3 spec.

Have a nice weekend