test/ruby/test_process.rb: reduce garbage during forks

* test/ruby/test_process.rb (test_deadlock_by_signal_at_forking):
  reduce garbage during forks

This seems to reduce failures on my memory-constrained VM
when doing a full test-all.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48147 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-10-27

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48148 b2dd03c8-39d4-4d8f-98ff-823fe69b080e