fix(mypy): Add django.contrib.auth to INSTALLED_APPS for mypy compatibility

Root cause analysis:
- After commit 5867e0c (dev package bump), mypy started failing with an
  AssertionError in mypy_django_plugin/transformers/auth.py
- The django-stubs plugin analyzes ALL Django type stubs, including
  django.contrib.auth.forms, even if the project doesn't directly use them
- When resolving the _User type alias in auth.forms, the plugin calls
  _get_abstract_base_user() which looks up AbstractBaseUser
- This lookup fails when django.contrib.auth is not in INSTALLED_APPS,
  causing sym.node to not be a TypeInfo

Why this doesn't affect other projects:
- Most Django projects include django.contrib.auth in INSTALLED_APPS by
  default (it's a standard contrib app)
- django-stubs' own test settings include auth in INSTALLED_APPS
- This project had only ["test_app"] in INSTALLED_APPS

The fix:
- Add django.contrib.contenttypes and django.contrib.auth to INSTALLED_APPS
  in tests/settings.py (contenttypes is a dependency of auth)
- Add mypy override for test_app to ignore no-untyped-call errors from
  django-extensions' AutoSlugField

Verified:
- mypy now passes: "Success: no issues found in 14 source files"
- All 6 tests still pass

Author: tony

pyproject.toml

@@ -141,6 +141,12 @@ module = [
 ]
 ignore_missing_imports = true
 
+[[tool.mypy.overrides]]
+module = [
+  "test_app.*",
+]
+disable_error_code = ["no-untyped-call"]
+
 [tool.coverage.run]
 branch = true
 parallel = true

tests/settings.py

@@ -11,6 +11,10 @@
     "default": {"NAME": ":memory:", "ENGINE": "django.db.backends.sqlite3"},
 }
 
-INSTALLED_APPS: list[str] = ["test_app"]
+INSTALLED_APPS: list[str] = [
+    "django.contrib.contenttypes",
+    "django.contrib.auth",
+    "test_app",
+]
 
 USE_TZ: bool = False