Require the swh.journal pytest plugin explicitly

conftest.py

+# Copyright (C) 2025  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
+
+pytest_plugins = ["swh.journal.pytest_plugin"]

requirements-test.txt

@@ -2,6 +2,7 @@ boto3-stubs
 botocore-stubs
 pytest >= 8.1
 swh.core[testing]
+swh.journal[pytest]
 types-confluent-kafka
 types-python-dateutil
 types-pyyaml