[BUG][Ruby] ApiError do not set the right error message

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 the API client get timeout and create an error with Connection timed out message
the error is then created with message Error message: the server returns an error
https://github.com/OpenAPITools/openapi-generator/blob/11515da0536dd3f72db3b20d5d4691da15f4b825/modules/openapi-generator/src/main/resources/ruby-client/api_client_typhoeus_partial.mustache#L15
https://github.com/OpenAPITools/openapi-generator/blob/11515da0536dd3f72db3b20d5d4691da15f4b825/modules/openapi-generator/src/main/resources/ruby-client/api_error.mustache#L37

I think it is because of the to_s overloading

openapi-generator version

gradle plugin 4.1.1

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Start with modules/openapi-generator/src/main/resources/ruby-client/api_client_typhoeus_partial.mustache and api_error.mustache at the linked lines, then inspect how ApiError.to_s is used. Reproduce the timeout case described in the issue and verify that the resulting error preserves the “Connection timed out” message instead of replacing it with the generic server-error text.