Consider backporting rackup fix #2706 to 3.39.x

[JonRowe]

👋 Thanks for all the hardwork team capybara!

We were debugging an issue with rspec-rails builds for Rails 7.1 on Ruby 2.7 (as we support the same matrix of Ruby as Rails does for each version) and it turned out it was due to the registration of the puma driver in capybara. Due to the change in minimum Ruby version for 3.40.0 we are forced to install 3.39.2 on Ruby 2.7 which lacks the patch from #2706.

We're attempting to patch this in our builds by overriding the puma driver but this means that "out of the box" Rails 7.1 with puma on 2.7 will still be broken, is there any chance of backporting the fix to a 3.39.3?

Meta

Capybara Version: 3.39.2

Expected Behavior

Freshly generated rails apps work with puma

Actual Behavior

 NameError:
     uninitialized constant Rack::Handler