Refs #25745 -- Isolated a foreign_object test.

tests/foreign_object/tests.py

 import datetime
 from operator import attrgetter
 
+from django.apps.registry import Apps
 from django.core.exceptions import FieldError
 from django.db import models
 from django.db.models.fields.related import ForeignObject
@@ -398,11 +399,14 @@ class MultiColumnFKTests(TestCase):
 class TestModelCheckTests(SimpleTestCase):
 
     def test_check_composite_foreign_object(self):
+        test_apps = Apps(['foreign_object'])
+
         class Parent(models.Model):
             a = models.PositiveIntegerField()
             b = models.PositiveIntegerField()
 
             class Meta:
+                apps = test_apps
                 unique_together = (('a', 'b'),)
 
         class Child(models.Model):
@@ -417,15 +421,21 @@ class TestModelCheckTests(SimpleTestCase):
                 related_name='children',
             )
 
+            class Meta:
+                apps = test_apps
+
         self.assertEqual(Child._meta.get_field('parent').check(from_model=Child), [])
 
     def test_check_subset_composite_foreign_object(self):
+        test_apps = Apps(['foreign_object'])
+
         class Parent(models.Model):
             a = models.PositiveIntegerField()
             b = models.PositiveIntegerField()
             c = models.PositiveIntegerField()
 
             class Meta:
+                apps = test_apps
                 unique_together = (('a', 'b'),)
 
         class Child(models.Model):
@@ -441,4 +451,7 @@ class TestModelCheckTests(SimpleTestCase):
                 related_name='children',
             )
 
+            class Meta:
+                apps = test_apps
+
         self.assertEqual(Child._meta.get_field('parent').check(from_model=Child), [])