🚨(backend) fix minor linting issues

Lint backend tests and sources.

src/backend/core/admin.py

@@ -6,7 +6,6 @@ from django.utils.translation import gettext_lazy as _
 from . import models
 
 
-
 class TemplateAccessInline(admin.TabularInline):
     """Inline admin class for template accesses."""
 

src/backend/core/tests/test_api_template_accesses.py

@@ -10,7 +10,6 @@ from rest_framework.test import APIClient
 from core import factories, models
 from core.api import serializers
 
-
 pytestmark = pytest.mark.django_db
 
 

src/backend/core/tests/test_api_users.py

@@ -7,7 +7,6 @@ from rest_framework.test import APIClient
 from core import factories, models
 from core.api import serializers
 
-
 pytestmark = pytest.mark.django_db