[DOCS] Fix capitalization (#74470) (#74502)

Co-authored-by: Robin Clarke <[email protected]>

Author: jrodewig

docs/reference/indices/split-index.asciidoc

@@ -192,7 +192,7 @@ the cluster state -- it doesn't wait for the split operation to start.
 
 Indices can only be split if they satisfy the following requirements:
 
-* the target index must not exist
+* The target index must not exist
 
 * The source index must have fewer primary shards than the target index.