Update version check in yaml test file for the bug fix for get index settings API (opensearch-project#16480)

Signed-off-by: Gao Binlong <gbinlong@amazon.com>

Author: gaobinlong

rest-api-spec/src/main/resources/rest-api-spec/test/indices.get_settings/40_number_of_routing_shards.yml

@@ -22,8 +22,8 @@ setup:
 ---
 Test retrieval of number_routing_shards settings:
   - skip:
-      version: " - 2.99.99"
-      reason: "introduced in 3.0.0" # TODO: change it to 2.18.0 after backport to 2.x branch
+      version: " - 2.18.99"
+      reason: "introduced in 2.19.0"
   - do:
       indices.get_settings:
         flat_settings: true