fix: input must be imported from six.moves not six

--HG--
branch : 3.26

cubicweb/server/schemaserial.py

@@ -23,7 +23,8 @@ import json
 import sys
 import sqlite3
 
-from six import PY2, text_type, string_types, input
+from six import PY2, text_type, string_types
+from six.moves import input
 
 from logilab.common.shellutils import ProgressBar, DummyProgressBar