chore: clean up running event loops after test

Author: xmatthias

tests/exchange/test_binance.py

@@ -1053,3 +1053,6 @@ async def mock_get_trade_hist(pair, *args, **kwargs):
 
     assert fetch_trades_cal[2][1]["params"][pagination_arg] != "0"
     assert fetch_trades_cal[3][1]["params"][pagination_arg] != "0"
+
+    # Clean up event loop to avoid warnings
+    exchange.close()