ci: replace super-linter with ruff

Super-linter ran from the unpinned :latest image and, because of
branches-ignore: [master], never on pull requests to master. Ruff now
checks syntax errors and pyflakes rules (E9, F) on every push and PR.

Fixes the existing findings: unused imports and variables, an unused
duplicate import in instances/tests.py, and the star import in
accounts/views.py. settings-dev.py keeps its star import of the base
settings.

interfaces/api/viewsets.py

@@ -1,7 +1,7 @@
 from admin.permissions import IsSuperUser
 from django.shortcuts import get_object_or_404
 from computes.models import Compute
-from rest_framework import status, viewsets
+from rest_framework import viewsets
 from rest_framework.response import Response
 from vrtManager.interface import wvmInterfaces, wvmInterface
 

interfaces/tests.py

@@ -1,3 +1,2 @@
-from django.test import TestCase
 
 # Create your tests here.