[BUG][Ruby] Pull Request #15162 Breaks Ruby Server Index Functionality

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• [x ] Have you validated the input using an OpenAPI validator (example)?
• [ x] Have you tested with the latest master to confirm the issue still exists?
• [ x] Have you searched for related issues/PRs?
• [x ] What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

openapi-generator version

6.6.0, regression

OpenAPI declaration file content or url

openapi: "3.0.3"
info:
  title: Service
  description: Service responsible for being a service
  version: "1.0"
servers:
  - url: http://localhost:8080
    description: local server
  - url: https://staging-server.example.com
    description: staging server
  - url: https://prod-server.example.com
    description: production server

paths:
  /v1/endpoint:
    $ref: "./api/v1/service.yaml#/~services"

Usage:

Client.configure do |config|
  config.access_token = @http_token
  config.server_index = 2
end

Generation Details

Steps to reproduce

In https://github.com/OpenAPITools/openapi-generator/pull/15162, functionality was removed that allowed retrieving a specific operation per server index. This change breaks the functionality of using server_index, causing the incorrect server to be retrieved.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/15162

Suggest a fix

Revert the commit causing the regression

Start by reviewing pull request #15162 and the Ruby server generation path related to server_index. Reproduce the issue with the provided OpenAPI declaration and configuration, then confirm that selecting a server index retrieves the corresponding operation and that the regression is resolved.