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.

instances/api/viewsets.py

@@ -290,7 +290,7 @@ class CreateInstanceViewSet(viewsets.ViewSet):
             volume_list.append(volume)
 
             with utils.libvirt_compute_lock(compute):
-                ret = conn.create_instance(
+                conn.create_instance(
                     name=serializer.validated_data["name"],
                     memory=serializer.validated_data["memory"],
                     vcpu=serializer.validated_data["vcpu"],

instances/test_disk_isolation.py

@@ -4,7 +4,7 @@ disk and media mutation views must be superuser-only (matching the UI, where
 the Disk tab is only rendered for superusers), and even for superusers the
 views must not act on volumes or option values taken blindly from the client.
 """
-from unittest.mock import MagicMock, patch
+from unittest.mock import patch
 
 from django.contrib.auth import get_user_model
 from django.test import TestCase

instances/test_security_mutations.py

@@ -271,7 +271,7 @@ class InstanceSecurityMutationsTestCase(TestCase):
 
         with patch("instances.utils.connection_manager.host_is_up", return_value=True), \
              patch("instances.utils.wvmInstances") as mock_instances_cls, \
-             patch("instances.utils.wvmInstance") as mock_instance_cls, \
+             patch("instances.utils.wvmInstance"), \
              patch("instances.utils.transaction.atomic"), \
              patch("instances.utils.Instance") as mock_instance_model:
 

instances/tests.py

@@ -10,7 +10,6 @@ from django.contrib.auth.models import Permission
 from django.http.response import Http404
 from django.shortcuts import reverse
 from django.test import TestCase
-from instances.views import instance
 from libvirt import VIR_DOMAIN_UNDEFINE_NVRAM
 from vrtManager.create import wvmCreate
 from vrtManager.util import randomUUID