tests: Avoid db fixture in debian build

swh/core/tests/test_logger.py

-# Copyright (C) 2015  The Software Heritage developers
+# Copyright (C) 2015-2018  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -33,6 +33,7 @@ def swh_db_logger(postgresql_proc, postgresql):
     return logger
 
 
+@pytest.mark.db
 def test_log(swh_db_logger, postgresql):
     logger = swh_db_logger
     modname = logger.name