[DOCS] Correct typo in split index API docs (elastic#48894)

Author: gaobinlong

docs/reference/indices/split-index.asciidoc

@@ -140,7 +140,7 @@ Indices can only be split if they satisfy the following requirements:
 
 * The index must have less primary shards than the target index.
 
-* The number of primary shards in the target index must be a factor of the
+* The number of primary shards in the target index must be a multiple of the
   number of primary shards in the source index.
 
 * The node handling the split process must have sufficient free disk space to
@@ -166,7 +166,7 @@ POST my_source_index/_split/my_target_index?copy_settings=true
 // CONSOLE
 // TEST[s/^/PUT my_source_index\n{"settings": {"index.blocks.write": true, "index.number_of_routing_shards" : 5, "index.number_of_shards": "1"}}\n/]
 
-<1> The number of shards in the target index. This must be a factor of the
+<1> The number of shards in the target index. This must be a multiple of the
     number of shards in the source index.