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.

storages/api/viewsets.py

@@ -3,7 +3,7 @@ from appsettings.settings import app_settings
 from computes.models import Compute
 from django.shortcuts import get_object_or_404
 from drf_spectacular.utils import extend_schema, inline_serializer
-from rest_framework import serializers, status, viewsets
+from rest_framework import serializers, viewsets
 from rest_framework.decorators import action
 from rest_framework.response import Response
 from vrtManager.storage import wvmStorage, wvmStorages

storages/views.py

@@ -290,8 +290,6 @@ def create_volume(request, compute_id, pool):
         compute.hostname, compute.login, compute.password, compute.type, pool
     )
 
-    storages = conn.get_storages()
-
     form = CreateVolumeForm(request.POST or None)
     if form.is_valid():
         data = form.cleaned_data