don't run the msgpack tests against the ZEO4 server

src/ZEO/tests/testZEO.py

@@ -1465,7 +1465,8 @@ def ClientDisconnected_errors_are_TransientErrors():
     True
     """
 
-if os.environ.get('ZEO_MSGPACK'):
+if not os.environ.get('ZEO4_SERVER'):
+    if os.environ.get('ZEO_MSGPACK'):
         def test_runzeo_msgpack_support():
             """
             >>> import ZEO
@@ -1476,7 +1477,7 @@ if os.environ.get('ZEO_MSGPACK'):
             'M5'
             >>> conn.close(); s()
             """
-else:
+    else:
         def test_runzeo_msgpack_support():
             """
             >>> import ZEO