test/rdoc/minitest_helper.rb: partially revert r66286

to resurrect r65613

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66299 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/rdoc/minitest_helper.rb

@@ -1,7 +1,8 @@
 # frozen_string_literal: true
+require 'bundler/errors'
 begin
   gem 'minitest', '~> 5.0'
-rescue NoMethodError, Gem::LoadError
+rescue NoMethodError, Gem::LoadError, Bundler::GemfileNotFound
   # for ruby tests
 end