Adjust the skip version for template mapping merging REST test.

rest-api-spec/src/main/resources/rest-api-spec/test/indices.put_index_template/15_composition.yml

@@ -204,8 +204,8 @@
 ---
 "Index template mapping merging":
   - skip:
-      version: " - 7.99.99"
-      reason: "index template v2 mapping merging not yet backported to 7.9"
+      version: " - 7.8.99"
+      reason: "index template v2 mapping merging not available before 7.9"
       features: allowed_warnings
 
   - do: