fix: tests

* test_banner_creation uses the active banner. the service method which
  is tested validates the data over the schema where start_datetime and
  end_datetime is a required field and it has to look like:
  '%Y-%m-%d %H:%M:%S'

* the problem is that test_read_banner uses the same banner to test the
  read service. the change in "active" has the effect that the stored
  value in the database is not like "2024-07-10 12:04:03.348391" which
  it is due the strftime function is not used. db.DateTime could only
  bring back the date in form of a datetime object which is then used in
  isoformat if the value in the database contains the ".34383" part.

* therefore the easiest solution is to use for test_read_banner the
  "other" banner

* ATTENTION: be cautious during the migration from utcnow to
  now(timezone.utc)

tests/services/test_services.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 #
 # Copyright (C) 2022 CERN.
+# Copyright (C) 2024 Graz University of Technology.
 #
 # Invenio-Banners is free software; you can redistribute it and/or modify it
 # under the terms of the MIT License; see LICENSE file for more details.
@@ -22,7 +23,10 @@
         "message": "active",
         "url_path": "/active",
         "category": "info",
-        "end_datetime": datetime.utcnow() + timedelta(days=1),
+        "start_datetime": datetime.utcnow().strftime("%Y-%m-%d %H:%M:%S"),
+        "end_datetime": (datetime.utcnow() + timedelta(days=1)).strftime(
+            "%Y-%m-%d %H:%M:%S"
+        ),
         "active": True,
     },
     "inactive": {
@@ -151,7 +155,7 @@ def test_delete_non_existing_banner(app, superuser_identity):
 def test_read_banner(app, simple_user_identity):
     """Read a banner by id."""
     # create banner first
-    banner = BannerModel.create(banners["active"])
+    banner = BannerModel.create(banners["other"])
 
     banner_result = service.read(simple_user_identity, banner.id)