[skip e2e] Fix grammar (#15011)

Signed-off-by: NBennu <yunmei.li@zilliz.com>

docs/design_docs/milvus_proto.md

@@ -750,7 +750,7 @@ message DescribeIndexResponse {
   // Response status
   common.Status status = 1;
 
-  // All index informations, for now only return tha latest index you created for the collection.
+  // All index informations, for now only return the latest index you created for the collection.
   repeated IndexDescription index_descriptions = 2;
 }
 ```