test_process.rb: suppress warnings

* test/ruby/test_process.rb (test_exec_close_reserved_fd):
  suppress "cannot close fd before spawn" warnings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51775 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_process.rb

@@ -2094,6 +2094,7 @@ EOS
       (3..6).each do |i|
         ret = run_in_child(<<-INPUT)
           begin
+            $VERBOSE = nil
             Process.exec('#{cmd}', 'dummy', #{i} => :close)
           rescue SystemCallError
           end