Fix deferrable RedshiftClusterSensor (apache#45098)

- Previously threw an exception that "'coroutine' object is not subscriptable".  Moving ["Clusters"] to the following line allows the result to parse into a subscriptable object.

providers/src/airflow/providers/amazon/aws/hooks/redshift_cluster.py

@@ -94,8 +94,8 @@ def cluster_status(self, cluster_identifier: str) -> str:
 
     async def cluster_status_async(self, cluster_identifier: str) -> str:
         async with self.async_conn as client:
-            response = await client.describe_clusters(ClusterIdentifier=cluster_identifier)["Clusters"]
-            return response[0]["ClusterStatus"] if response else None
+            response = await client.describe_clusters(ClusterIdentifier=cluster_identifier)
+            return response["Clusters"][0]["ClusterStatus"] if response else None
 
     def delete_cluster(
         self,