[3.11] gh-99357: Close the event loop when it is no longer used in test_uncancel_structured_blocks (GH-99414) (#99424)

(cherry picked from commit 99972dc745)

Co-authored-by: Xiao Chen <chenxiao_7@163.com>

Lib/test/test_asyncio/test_tasks.py

@@ -639,6 +639,7 @@ class BaseTaskTests:
             await asyncio.sleep(0)
             return timed_out, structured_block_finished, outer_code_reached
 
+        try:
             # Test which timed out.
             t1 = self.new_task(loop, make_request_with_timeout(sleep=10.0, timeout=0.1))
             timed_out, structured_block_finished, outer_code_reached = (
@@ -660,6 +661,8 @@ class BaseTaskTests:
             self.assertTrue(structured_block_finished)
             self.assertTrue(outer_code_reached)
             self.assertEqual(t2.cancelling(), 0)
+        finally:
+            loop.close()
 
     def test_cancel(self):