mq: don't refer to a random name-captured repo object

Previously, we used a repo object captured at the time of monkeypatching.

hgext/mq.py

@@ -3436,7 +3436,7 b' def reposetup(ui, repo):'
                             outapplied.pop()
                 # looking for pushed and shared changeset
                 for node in outapplied:
-                    if repo[node].phase() < phases.secret:
+                    if self[node].phase() < phases.secret:
                         raise util.Abort(_('source has mq patches applied'))
                 # no non-secret patches pushed
             super(mqrepo, self).checkpush(force, revs)