fix typo, my-app -> my_app (#96543) (#96549)

fix typo, `my-app` -> `my_app`

Co-authored-by: Joe Wu <[email protected]>

Author: abdonpijpelink

docs/reference/search-application/apis/put-search-application.asciidoc

@@ -91,7 +91,7 @@ PUT _application/search_application/my-app?create
 ----
 // TEST[skip:TBD]
 
-The following example creates or updates an existing Search Application called `my_app`:
+The following example creates or updates an existing Search Application called `my-app`:
 
 [source,console]
 ----