Clear transaction syncs earlier

To mitigate errors during tearDown.

Lots of tests are sloppy about closing connection (because they could
be), but storages tend to get closed and transactions aborted. This
has the effedt of calling afterCompletion on connections which tries
to call storage lastTransaction, which causes errors.

src/ZODB/tests/util.py

@@ -73,8 +73,8 @@ def setUp(test, name='test'):
     zope.testing.setupstack.register(test, transaction.abort)
 
 def tearDown(test):
-    zope.testing.setupstack.tearDown(test)
     clear_transaction_syncs()
+    zope.testing.setupstack.tearDown(test)
 
 class TestCase(unittest.TestCase):