Fix noisy log message about missing mappings

From the scheduler integration test

Original commit: elastic/x-pack-elasticsearch@02d3f58d83

elasticsearch/src/test/resources/rest-api-spec/test/start_stop_scheduler.yaml

@@ -2,6 +2,12 @@ setup:
   - do:
       indices.create:
         index: airline-data
+        body:
+          mappings:
+            response:
+              properties:
+                time:
+                  type: date
 
   - do:
       xpack.ml.put_job: