[5.2.x] Added SimpleTestCase.enterContext() on Python < 3.11.

This reverts commit 47a618d45c6e40dd59f4cdd46fd5fc7d11626f6d and uses
a solution similar to ed4f83782d9f3404ad600f6131ef78244ff1e162 instead.

django/test/testcases.py

@@ -404,6 +404,10 @@ class SimpleTestCase(unittest.TestCase):
         def enterClassContext(cls, cm):
             return _enter_context(cm, cls.addClassCleanup)
 
+        # Backport of unittest.TestCase.enterContext() from Python 3.11.
+        def enterContext(self, cm):
+            return _enter_context(cm, self.addCleanup)
+
     def settings(self, **kwargs):
         """
         A context manager that temporarily sets a setting and reverts to the

tests/composite_pk/test_filter.py

@@ -14,7 +14,6 @@ from django.db.models import (
 from django.db.models.functions import Cast
 from django.db.models.lookups import Exact
 from django.test import TestCase, skipUnlessDBFeature
-from django.utils.version import PY311
 
 from .models import Comment, Tenant, User
 
@@ -557,10 +556,4 @@ class CompositePKFilterTupleLookupFallbackTests(CompositePKFilterTests):
         feature_patch = patch.object(
             connection.features, "supports_tuple_lookups", False
         )
-        if PY311:
-            self.enterContext(feature_patch)
-        else:
-            # unittest.TestCase.enterContext() was added in Python 3.11.
-            from django.test.testcases import _enter_context
-
-            _enter_context(feature_patch, self.addCleanup)
+        self.enterContext(feature_patch)