fix: update test server for Rack 3.x compatibility

Author: georgeguimaraes

Gemfile

@@ -17,6 +17,7 @@ gem 'em-http-request',    '>= 1.1'
 gem 'rake',               '>= 13.0'
 gem 'rspec',              '>= 3.1'
 gem 'sinatra',            '>= 3.0'
+gem 'rackup'
 gem 'webrick'
 
 eval_gemfile 'gemfiles/rubocop.gemfile'

spec/support/test_server.rb

@@ -32,7 +32,8 @@ def run!
         Logger: WEBrick::Log.new(log),
         AccessLog: [[log, '[%{X-Faraday-Adapter}i] %m  %U  ->  %s %b']]
       }
-      Rack::Handler::WEBrick.run(TestApp, **webrick_opts)
+      handler = defined?(Rackup::Handler) ? Rackup::Handler::WEBrick : Rack::Handler::WEBrick
+      handler.run(TestApp, **webrick_opts)
     end
   end