test_env.rb: relax limits

* test/ruby/test_env.rb (test_memory_leak_{aset,select,shift}):
  increase rehearsals and memory leak limits.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46595 b2dd03c8-39d4-4d8f-98ff-823fe69b080e