[BUG][Go] Content type selection breaks when multiple content types present

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

When API returns mixed content - 200 returns File/Binary and 500 returns JSON which is typical for error handling.
Generated code will include two accept headers. Problem is that selectHeaderAccept function that builds headers always forces accept headers to be JSON. As result server responses crash as server only knows how to set zip content type.

https://github.com/redhat-developer/app-services-sdk-go/blob/main/registryinstance/apiv1internal/client/api_admin.go#L1004-L1007

HTTPHeaderAccepts := []string{"application/zip", "application/json"}

openapi-generator version

5.2.1

OpenAPI declaration file content or URL

https://github.com/redhat-developer/app-services-sdk-go/blob/main/.openapi/registry-instance.json#L651-L665

Steps to reproduce

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/10337

Suggest a fix

Start with the generated registryinstance/apiv1internal/client/api_admin.go selectHeaderAccept call and compare it with the content definitions in .openapi/registry-instance.json. Review related pull request 10337 for existing context, then trace the corresponding OpenAPI Generator logic. Done means generated Go clients handle the mixed binary and JSON responses without forcing the wrong content type, with regression coverage.