dtrace: wait command

* test/dtrace/helper.rb (DTrace::TestCase::READ_PROBES): wait
  the spawned command not to make a waiter thread.  fix up r55736.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55762 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/dtrace/helper.rb

@@ -31,9 +31,12 @@ module DTrace
       DTRACE_CMD = %w[dtrace -b 8m]
     when /darwin/i
       READ_PROBES = proc do |cmd|
-        PTY.spawn(*cmd) do |io, _|
-          break io.readlines.each {|line| line.sub!(/\r$/, "")}
+        lines = nil
+        PTY.spawn(*cmd) do |io, _, pid|
+          lines = io.readlines.each {|line| line.sub!(/\r$/, "")}
+          Process.wait(pid)
         end
+        lines
       end
     end