🚨(CI) fix linter backend

The linter in the CI was checking only the
impress directory. We were passing near some lint
issues. Now the linter checks the whole backend
directory.

src/backend/demo/tests/test_commands_create_demo.py

@@ -1,7 +1,5 @@
 """Test the `create_demo` management command"""
 
-from unittest import mock
-
 from django.core.management import call_command
 from django.test import override_settings