tests: django: Fix a warning related timezone settings

The warning is:

RemovedInDjango50Warning: The default value of USE_TZ will change from False to
True in Django 5.0. Set USE_TZ to False in your project settings if you want to
keep the current default behavior.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/tests/data/django_test_settings.py

@@ -56,3 +56,7 @@ TEMPLATES = [{
     'APP_DIRS': True,
     'DIRS': ['plinth/tests/data/templates/'],
 }]
+
+TIME_ZONE = 'UTC'
+
+USE_TZ = True

plinth/tests/test_notification.py

@@ -386,7 +386,7 @@ def test_display_context(gettext, note, user, rf):
     assert context_note['actions'] == expected_actions
     assert context_note['data'] == expected_data
     assert note.data == data
-    now = datetime.datetime.now()
+    now = datetime.datetime.now(datetime.timezone.utc)
     assert (now - context_note['created_time']).seconds < 60
     assert (now - context_note['last_update_time']).seconds < 60
     assert context_note['user'] == 'test-user'