Mitigate test flakiness.

Author: aaugustin

tests/asyncio/test_server.py

@@ -542,7 +542,8 @@ async def test_close_server_keeps_handlers_running(self):
                     async with asyncio_timeout(2 * MS):
                         await server.wait_closed()
 
-                async with asyncio_timeout(3 * MS):
+                # Set a large timeout here, else the test becomes flaky.
+                async with asyncio_timeout(5 * MS):
                     await server.wait_closed()