py3: add test-dirstate-race2.t to list of passing tests

This test was added new recently. The py3 buildbot found that it passes, so
let's add it to the list of passing tests.

Differential Revision: https://phab.mercurial-scm.org/D6530

contrib/python3-whitelist

@@ -164,6 +164,7 b' test-directaccess.t'
 test-dirstate-backup.t
 test-dirstate-nonnormalset.t
 test-dirstate-race.t
+test-dirstate-race2.t
 test-dirstate.t
 test-dispatch.py
 test-dispatch.t