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 Ruby rails-cloudsql examples for Google App Engine flexible environment. It updates the required Ruby version to 3.2.0 or newer and configures the App Engine deployment to use Ubuntu 22. These changes ensure compatibility with the latest Rails versions and align the examples with current best practices, while also adjusting the CI pipeline to correctly test these updated configurations.

Highlights

• Ruby Version Update: The rails-cloudsql examples for both MySQL and PostgreSQL now explicitly require Ruby version 3.2.0 or newer in their Gemfiles.
• App Engine Runtime Configuration: The app.yaml files for the rails-cloudsql examples have been updated to specify ubuntu22 as the operating system in the runtime_config.
• CI Pipeline Adjustment: The Kokoro CI configuration has been modified to ensure that the rails-cloudsql examples are tested only with the newest Ruby version, aligning with their Rails 7 and Ruby 3.2+ requirements, and are excluded from runs using older Ruby versions.

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[gemini-code-assist]

Code Review

This pull request modernizes the rails-cloudsql examples for App Engine Flex by updating them to use Ruby 3.2 and the Ubuntu 22 operating system. The changes to the Gemfile and app.yaml files are appropriate for this goal. The CI configuration in .toys/kokoro-ci.rb is also updated to ensure these modernized examples are tested with the correct Ruby version. I have added a comment with a suggestion to improve the maintainability and readability of the CI script by refactoring repeated code.

[gemini-code-assist]

This logic can be improved for readability and maintainability. The directory names are repeated from earlier in the file (lines 157-158) and the chained != checks are less clear than using Array#include?.

Consider defining the list of cloudsql directories as a constant or local variable at a higher scope, for example:

CLOUDSQL_DIRS = %w[
  appengine/rails-cloudsql-postgres
  appengine/rails-cloudsql-mysql
].freeze

Then you could use it to simplify the logic in both places. Here, it would look like this:

@products.delete_if do |dir|
  dir.start_with?("appengine/") && !CLOUDSQL_DIRS.include?(dir)
end

And on lines 157-158, the deletion could be simplified to:

CLOUDSQL_DIRS.each { |dir| @products.delete dir }

This would make the code DRY and easier to update.