asyncio/tests: Fix a ResourceWarning due to unclosed loop
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index 47b17d1..5ee20f6 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -2212,6 +2212,10 @@
         self.loop = asyncio.new_event_loop()
         asyncio.set_event_loop(None)
 
+    def tearDown(self):
+        self.loop.close()
+        self.loop = None
+
     def test_sleep_zero(self):
         result = 0