test: add small wait to reduce test flakyness

Author: xmatthias

tests/exchange/test_exchange_ws.py

@@ -101,6 +101,7 @@ async def sleeper(*args, **kwargs):
         time_machine.shift(timedelta(minutes=5))
         await asyncio.sleep(0.1)
         exchange_ws.schedule_ohlcv("ETH/BTC", "1m", CandleType.SPOT)
+        await asyncio.sleep(0.1)
         # XRP/BTC should be cleaned up.
         assert exchange_ws._klines_watching == {
             ("ETH/BTC", "1m", CandleType.SPOT),