Stop using at_exit to shutdown playwright

The processes of Playwright and headless browser can stop when the ruby
process terminates.

Author: mrkn

lib/charty/backends/backend_helpers/playwright_manager.rb

@@ -57,10 +57,6 @@ module PlaywrightManager
           @_context = nil
           @_browser = nil
         end
-
-        at_exit do
-          shutdown
-        end
       end
     end
   end

test/run.rb

@@ -16,13 +16,4 @@
 
 require_relative "helper"
 
-result = Test::Unit::AutoRunner.run(true, test_dir.to_s)
-
-if defined? Charty::Backends::BackendHelpers::PlaywrightManager
-  require "timeout"
-  Timeout.timeout(60) do
-    Charty::Backends::BackendHelpers::PlaywrightManager.shutdown
-  end
-end
-
-exit(result)
+exit(Test::Unit::AutoRunner.run(true, test_dir.to_s))