* test/ruby/test_require.rb: improve test for r38744.
  fix to use Tempfile instead of temporary file in current directory.
  the patch is from nobu (Nobuyoshi Nakada).

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38745 b2dd03c8-39d4-4d8f-98ff-823fe69b080e