define _connect_to_sentinel in async server

Author: agnesnatasya

redis/asyncio/sentinel.py

@@ -73,6 +73,9 @@ async def _connect_retry(self):
         if self._is_address_fixed:
             self.connect_to(self.host, self.port)
             return
+        await self._connect_to_sentinel()
+    
+    async def _connect_to_sentinel(self):
         # If same_server is False, connnect to master in master mode
         # and rotate to the next slave in slave mode
         if self.connection_pool.is_master: