bpo-42553: Fix test_asyncio.test_call_later() (GH-23627)

Fix test_asyncio.test_call_later() race condition: don't measure
asyncio performance in the call_later() unit test. The test failed
randomly on the CI.
(cherry picked from commit 7e5e13d)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: miss-islington

Lib/test/test_asyncio/test_events.py

@@ -293,11 +293,8 @@ def callback(arg):
             self.loop.stop()
 
         self.loop.call_later(0.1, callback, 'hello world')
-        t0 = time.monotonic()
         self.loop.run_forever()
-        t1 = time.monotonic()
         self.assertEqual(results, ['hello world'])
-        self.assertTrue(0.08 <= t1-t0 <= 0.8, t1-t0)
 
     def test_call_soon(self):
         results = []

Misc/NEWS.d/next/Tests/2020-12-03-13-32-44.bpo-42553.2TRE2N.rst

@@ -0,0 +1,3 @@
+Fix ``test_asyncio.test_call_later()`` race condition: don't measure asyncio
+performance in the ``call_later()`` unit test. The test failed randomly on
+the CI.