Prevent a warning: assigned but unused variable - out

http://rubyci.s3.amazonaws.com/ubuntu1804/ruby-master/log/20220613T003003Z.log.html.gz
```
/home/chkbuild/chkbuild/tmp/build/20220613T003003Z/ruby/test/ruby/test_yjit_exit_locations.rb:96: warning: assigned but unused variable - out
/home/chkbuild/chkbuild/tmp/build/20220613T003003Z/ruby/test/ruby/test_yjit_exit_locations.rb:96: warning: assigned but unused variable - err
/home/chkbuild/chkbuild/tmp/build/20220613T003003Z/ruby/test/ruby/test_yjit_exit_locations.rb:96: warning: assigned but unused variable - status
```

test/ruby/test_yjit_exit_locations.rb

@@ -93,9 +93,9 @@ class TestYJITExitLocations < Test::Unit::TestCase
     ]
     args << "-e" << script_shell_encode(script)
     stats_r, stats_w = IO.pipe
-    out, err, status = EnvUtil.invoke_ruby(args,
-                                           '', true, true, timeout: 1000, ios: { 3 => stats_w }
-                                          )
+    _out, _err, _status = EnvUtil.invoke_ruby(args,
+                                              '', true, true, timeout: 1000, ios: { 3 => stats_w }
+                                             )
     stats_w.close
     stats = stats_r.read
     stats = Marshal.load(stats) if !stats.empty?