pythongh-131707: fix unawaited coroutine warning in test_coroutines.Corouti… (python#131708)

pythongh-131707: fix unawaited coroutine warning in test_coroutines.CoroutineTest.test_17

Author: graingert

Lib/test/test_coroutines.py

@@ -1199,8 +1199,8 @@ async def __anext__(self):
             def __aiter__(self):
                 return self
 
-        anext_awaitable = anext(A(), "a").__await__()
-        self.assertRaises(TypeError, anext_awaitable.close, 1)
+        with contextlib.closing(anext(A(), "a").__await__()) as anext_awaitable:
+            self.assertRaises(TypeError, anext_awaitable.close, 1)
 
     def test_with_1(self):
         class Manager: