test_fork.rb: wait signals

* bootstraptest/test_fork.rb: wait until receiving both singals,
  upto 0.1sec.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46606 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bootstraptest/test_fork.rb

@@ -66,6 +66,7 @@ assert_equal '[1, 2]', %q{
       Process.kill(:TERM, pid)
     end
     Process.wait(pid)
+    100.times {break if a.size > 1; sleep 0.001}
     a.sort
   rescue NotImplementedError
     [1, 2]