Fix: make Railtie compatible with Rails 8 by removing sqlite3_production_warning

[ajitdsa]

Summary

This PR fixes a compatibility issue with Rails 8.
In Rails 8, the sqlite3_production_warning configuration key and its writer method (ActiveRecord::Base.sqlite3_production_warning=) were removed.
The current litestack Railtie still sets this flag unconditionally, which causes Rails 8 applications to fail at boot with:

Changes

• Update lib/litestack/railtie.rb initializer:
  • On Rails < 8: keep existing behavior (sqlite3_production_warning = false).
  • On Rails ≥ 8: remove the key from config.active_record so ActiveRecord does not attempt to apply it.

Why

The entire purpose of litestack is to make SQLite production-ready. Disabling the Rails “don’t use SQLite in production” warning is still important for Rails 6/7.
However, since Rails 8 removed this config entirely, litestack should not attempt to set it anymore.

Impact

• Rails 6/7: behavior unchanged.
• Rails 8: litestack loads without error, and applications can run normally.

Example

Before this change, Rails 8 apps using litestack crashed during boot.
After applying this change, the same apps boot cleanly:

# Gemfile
gem "litestack", github: "oldmoe/litestack", branch: "rails8-fix"

One more note:

In my app, I had added some debugging in my config/application.rb thusly:

config.after_initialize do
  keys =
    if config.active_record.respond_to?(:to_h)
      config.active_record.to_h.keys
    elsif config.active_record.respond_to?(:each_pair)
      k = []
      config.active_record.each_pair { |key, _| k << key }
      k
    else
      []
    end
  Rails.logger.warn("AR config keys: #{keys.inspect}")
end

With this PR, sqlite3_production_warning was not included in the keys in my Rails 8 app.