refactor: Modernize CI with Appraisal gem and consolidate workflows

- Add Appraisal gem for managing multiple test gemfiles
- Create test matrix for Rails 6.1-8.0 and ActiveAdmin 2.9-4.x
- Consolidate multiple workflow files into single ci.yml
- Use matrix strategy to test across Ruby 3.0-3.3
- Remove deprecated individual workflow files
- Add gemfiles/ to gitignore as they're generated
- Improve backward compatibility support

spec/support/javascript_helper.rb

@@ -7,6 +7,7 @@ module JavaScriptHelper
       loop do
         quill_loaded = page.evaluate_script('typeof Quill !== "undefined"')
         break if quill_loaded
+
         sleep 0.1
       end
     end
@@ -20,6 +21,7 @@ module JavaScriptHelper
           typeof getQuillEditorByElementId === 'function'
         JS
         break if init_loaded
+
         sleep 0.1
       end
     end
@@ -93,6 +95,7 @@ module JavaScriptHelper
   def quill_has_content?(text, index = 0)
     content = get_quill_content(index)
     return false unless content
+
     content.include?(text)
   end
 
@@ -115,4 +118,4 @@ end
 
 RSpec.configure do |config|
   config.include JavaScriptHelper, type: :system
-end
+end