need bigdecimal and mutex_m for ruby >= 3.4

Author: toy

Appraisals

@@ -21,6 +21,11 @@ def appgen(gems) # rubocop:disable Metrics/CyclomaticComplexity
       gem 'loofah', '< 2.21.0'
     end
 
+    if RUBY_VERSION >= '3.4'
+      gem 'bigdecimal'
+      gem 'mutex_m'
+    end
+
     gem 'tzinfo'
 
     gem 'sprockets-rails' if gems['railties'] != '~> 3.2' && !gems['sprockets-rails']