Add ostruct to Gemfile for Ruby >= 3.3.5

Gemfile

@@ -62,6 +62,11 @@ if RUBY_VERSION >= '2.6.0'
   gem 'rubocop-rspec', ['~> 2.20', '< 2.21'], require: false
 end
 
+if RUBY_VERSION >= '3.3'
+  gem 'fiddle'
+  gem 'ostruct'
+end
+
 # Optional extensions
 # TODO: Move this to Appraisals?
 # dogstatsd v5, but lower than 5.2, has possible memory leak with datadog.