Fix typo in cluster module docs

This commit fixes a simple typo in the cluster module docs.

Closes #19393

docs/reference/modules/cluster.asciidoc

@@ -7,7 +7,7 @@ cluster.
 
 There are a number of settings available to control the shard allocation process:
 
-*   <<shards-allocation>> lists the settings to control the allocation an
+*   <<shards-allocation>> lists the settings to control the allocation and
     rebalancing operations.
 
 *   <<disk-allocator>> explains how Elasticsearch takes available disk space