Fixed #30023 -- Prevented SQLite schema alterations while foreign key checks are enabled.

Prior to this change foreign key constraint references could be left pointing
at tables dropped during operations simulating unsupported table alterations
because of an unexpected failure to disable foreign key constraint checks.

SQLite3 does not allow disabling such checks while in a transaction so they
must be disabled beforehand.

Thanks ezaquarii for the report and Carlton and Tim for the review.

tests/model_options/test_tablespaces.py

@@ -1,7 +1,9 @@
 from django.apps import apps
 from django.conf import settings
 from django.db import connection
-from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
+from django.test import (
+    TransactionTestCase, skipIfDBFeature, skipUnlessDBFeature,
+)
 
 from .models.tablespaces import (
     Article, ArticleRef, Authors, Reviewers, Scientist, ScientistRef,
@@ -21,7 +23,8 @@ def sql_for_index(model):
 # We can't test the DEFAULT_TABLESPACE and DEFAULT_INDEX_TABLESPACE settings
 # because they're evaluated when the model class is defined. As a consequence,
 # @override_settings doesn't work, and the tests depend
-class TablespacesTests(TestCase):
+class TablespacesTests(TransactionTestCase):
+    available_apps = ['model_options']
 
     def setUp(self):
         # The unmanaged models need to be removed after the test in order to