GH-89369: test_contextlib_async finalizes event loop after each test (GH-93074)

Use asyncio.run().
(cherry picked from commit d2ef66a10b)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>

Lib/test/test_contextlib_async.py

@@ -14,15 +14,12 @@ def _async_test(func):
     @functools.wraps(func)
     def wrapper(*args, **kwargs):
         coro = func(*args, **kwargs)
-        loop = asyncio.new_event_loop()
-        asyncio.set_event_loop(loop)
-        try:
-            return loop.run_until_complete(coro)
-        finally:
-            loop.close()
-            asyncio.set_event_loop_policy(None)
+        asyncio.run(coro)
     return wrapper
 
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
 
 class TestAbstractAsyncContextManager(unittest.TestCase):