bpo-38248: Fix inconsistent immediate asyncio.Task cancellation (GH-16330)

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index a0cb884..38d9827 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -284,7 +284,7 @@
             if self._must_cancel:
                 # Task is cancelled right before coro stops.
                 self._must_cancel = False
-                super().set_exception(exceptions.CancelledError())
+                super().cancel()
             else:
                 super().set_result(exc.value)
         except exceptions.CancelledError: