Correctly invoke update from CassandraBatchOperations.update.

Previously, we've called `insert` instead of `update`.

Closes #1534

Author: mp911de

spring-data-cassandra/src/main/java/org/springframework/data/cassandra/core/CassandraBatchOperations.java

@@ -159,7 +159,7 @@ default CassandraBatchOperations update(Object entity, WriteOptions options) {
 
 		Assert.notNull(entity, "Entity must not be null");
 
-		return insert(Collections.singleton(entity), options);
+		return update(Collections.singleton(entity), options);
 	}
 
 	/**

spring-data-cassandra/src/main/java/org/springframework/data/cassandra/core/ReactiveCassandraBatchOperations.java

@@ -210,7 +210,7 @@ default ReactiveCassandraBatchOperations update(Object entity, WriteOptions opti
 
 		Assert.notNull(entity, "Entity must not be null");
 
-		return insert(Collections.singleton(entity), options);
+		return update(Collections.singleton(entity), options);
 	}
 
 	/**