[bundler/bundler] Enable retries on flaky spec

https://github.com/bundler/bundler/commit/da360659f7

spec/bundler/realworld/double_check_spec.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-RSpec.describe "double checking sources", :realworld => true do
+RSpec.describe "double checking sources", :realworld => true, :sometimes => true do
   it "finds already-installed gems" do
     create_file("rails.gemspec", <<-RUBY)
       Gem::Specification.new do |s|