Extend the version range to run flat-object field REST Yaml test on 2.7.0 (#7081) (#7083)

(cherry picked from commit 312bc82)

Signed-off-by: Mingshi Liu <mingshl@amazon.com>

Author: opensearch-trigger-bot[bot]

modules/lang-painless/src/yamlRestTest/resources/rest-api-spec/test/painless/30_search.yml

@@ -487,8 +487,8 @@
 
 "Flat-object fields from within the scripting":
   - skip:
-      version: " - 2.99.99"
-      reason: "flat_object is introduced in 3.0.0 in main branch"
+      version: " - 2.6.99"
+      reason: "flat_object is introduced in 2.7.0"
 
   - do:
       indices.create:

rest-api-spec/src/main/resources/rest-api-spec/test/index/90_flat_object.yml

@@ -80,8 +80,8 @@ teardown:
 # and no dynamic fields were created.
 "Mappings":
   - skip:
-      version: " - 2.99.99"
-      reason: "flat_object is introduced in 3.0.0 in main branch"
+      version: " - 2.6.99"
+      reason: "flat_object is introduced in 2.7.0"
 
   - do:
       indices.get_mapping: