fix(appengine): modernize rails-cloudsql gae flex ruby examples

[palladius]

Fixes #1671. Replaces and closes #1475 and #1477.

[gemini-code-assist]

Summary of Changes

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This pull request modernizes the App Engine Flex Ruby examples for Rails Cloud SQL (PostgreSQL and MySQL). The updates involve specifying a minimum Ruby version of 3.2.0 and setting the operating system to Ubuntu 22 in their respective configurations. These changes ensure the examples leverage current technologies and are correctly integrated into the CI pipeline, which has been updated to run these specific examples only on the newest Ruby environment.

Highlights

• Modernized App Engine Flex Ruby Examples: The rails-cloudsql-mysql and rails-cloudsql-postgres examples have been updated to use more recent technologies, specifically Rails 7.
• Ruby Version Requirement: Both rails-cloudsql examples now explicitly require Ruby version 3.2.0 or newer in their Gemfiles to align with Rails 7 compatibility.
• Operating System Specification: The app.yaml configurations for both rails-cloudsql examples now specify ubuntu22 as the operating system for their runtime environment.
• CI Configuration Update: The Kokoro CI configuration has been adjusted to ensure that these rails-cloudsql examples are tested only with the newest Ruby version, aligning with their updated Rails 7 and Ruby 3.2+ requirements.

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[gemini-code-assist]

Code Review

This pull request modernizes the Rails Cloud SQL examples for App Engine Flex by updating them to use a newer Ruby version (>= 3.2.0) and a more recent operating system image (ubuntu22). The CI configuration in .toys/kokoro-ci.rb has been adjusted accordingly to ensure these examples are tested with the newest Ruby version. The changes are logical and well-implemented. I've added one suggestion to improve the maintainability of the CI script by reducing code repetition.

[gemini-code-assist]

This condition can be simplified by checking for inclusion in an array of the rails-cloudsql samples. This improves readability and makes it easier to add more exceptions in the future. A similar list of samples is used on lines 157-158; using an array here could be the first step toward removing that duplication by defining the array once and using it in both places.

    @products.delete_if do |dir|
      dir.start_with?("appengine/") &&
        !["appengine/rails-cloudsql-postgres",
          "appengine/rails-cloudsql-mysql"].include?(dir)
    end

[palladius]

I've addressed the simplification by isolating the array, and resolved the RuboCop formatting offenses inside the .toys/kokoro-ci.rb script which tripped both Kokoro test matrices up! Tests should be unblocked now.
-- Antigravity@ricc-mac on behalf of Riccardo 💛 🚀