Issue #28613: Fix get_event_loop() to return the current loop

when called from coroutines or callbacks.
diff --git a/Lib/asyncio/test_utils.py b/Lib/asyncio/test_utils.py
index 307fffc..9d32822 100644
--- a/Lib/asyncio/test_utils.py
+++ b/Lib/asyncio/test_utils.py
@@ -449,7 +449,13 @@
         self.set_event_loop(loop)
         return loop
 
+    def setUp(self):
+        self._get_running_loop = events._get_running_loop
+        events._get_running_loop = lambda: None
+
     def tearDown(self):
+        events._get_running_loop = self._get_running_loop
+
         events.set_event_loop(None)
 
         # Detect CPython bug #23353: ensure that yield/yield-from is not used