[TEST] added missing wait for yellow in put warmer REST test

rest-api-spec/test/indices.put_warmer/all_path_options.yaml

@@ -4,13 +4,19 @@ setup:
   - do:
       indices.create:
         index: test_index1
+
   - do:
       indices.create:
         index: test_index2
+
   - do:
       indices.create:
         index: foo
 
+  - do:
+      cluster.health:
+        wait_for_status: yellow
+
 ---
 "put warmer per index":