Fixed #27236 -- Deprecated Meta.index_together in favor of Meta.indexes.

This also deprecates AlterIndexTogether migration operation.

tests/check_framework/test_migrations.py

@@ -1,7 +1,11 @@
+from unittest.mock import ANY
+
 from django.core import checks
+from django.core.checks.migrations import check_migration_operations
 from django.db import migrations
 from django.db.migrations.operations.base import Operation
 from django.test import TestCase
+from django.test.utils import override_settings
 
 
 class DeprecatedMigrationOperationTests(TestCase):
@@ -50,6 +54,23 @@ class DeprecatedMigrationOperationTests(TestCase):
             ],
         )
 
+    @override_settings(
+        INSTALLED_APPS=["check_framework.migrations_test_apps.index_together_app"]
+    )
+    def tests_check_alter_index_together(self):
+        errors = check_migration_operations()
+        self.assertEqual(
+            errors,
+            [
+                checks.Warning(
+                    "AlterIndexTogether is deprecated. Support for it (except in "
+                    "historical migrations) will be removed in Django 5.1.",
+                    obj=ANY,
+                    id="migrations.W001",
+                )
+            ],
+        )
+
 
 class RemovedMigrationOperationTests(TestCase):
     def test_default_operation(self):