Prevented TestNoInitialDataLoading to pollute other tests (Refs #15926)

Tests were still failing with MySQL. It seems a rollback is solving
the issue.

tests/modeltests/fixtures_model_package/tests.py

@@ -1,5 +1,6 @@
 from django.core import management
-from django.test import TestCase
+from django.db import transaction
+from django.test import TestCase, TransactionTestCase
 
 from .models import Article, Book
 
@@ -20,16 +21,18 @@ class SampleTestCase(TestCase):
         )
 
 
-class TestNoInitialDataLoading(TestCase):
+class TestNoInitialDataLoading(TransactionTestCase):
     def test_syncdb(self):
-        Book.objects.all().delete()
+        with transaction.commit_manually():
+            Book.objects.all().delete()
 
-        management.call_command(
-            'syncdb',
-            verbosity=0,
-            load_initial_data=False
-        )
-        self.assertQuerysetEqual(Book.objects.all(), [])
+            management.call_command(
+                'syncdb',
+                verbosity=0,
+                load_initial_data=False
+            )
+            self.assertQuerysetEqual(Book.objects.all(), [])
+            transaction.rollback()
 
     def test_flush(self):
         # Test presence of fixture (flush called by TransactionTestCase)
@@ -40,13 +43,16 @@ class TestNoInitialDataLoading(TestCase):
             lambda a: a.name
         )
 
-        management.call_command(
-            'flush',
-            verbosity=0,
-            interactive=False,
-            load_initial_data=False
-        )
-        self.assertQuerysetEqual(Book.objects.all(), [])
+        with transaction.commit_manually():
+            management.call_command(
+                'flush',
+                verbosity=0,
+                interactive=False,
+                commit=False,
+                load_initial_data=False
+            )
+            self.assertQuerysetEqual(Book.objects.all(), [])
+            transaction.rollback()
 
 
 class FixtureTestCase(TestCase):