Fix CCS stats test (#115801)

Set index stats to be refreshed immediately - cached 0 size may be the
reason why it fails.

Fixes #115600

Author: smalyshev

muted-tests.yml

@@ -236,9 +236,6 @@ tests:
 - class: org.elasticsearch.smoketest.DocsClientYamlTestSuiteIT
   method: test {yaml=reference/esql/esql-across-clusters/line_197}
   issue: https://github.com/elastic/elasticsearch/issues/115575
-- class: org.elasticsearch.xpack.security.CoreWithSecurityClientYamlTestSuiteIT
-  method: test {yaml=cluster.stats/30_ccs_stats/cross-cluster search stats search}
-  issue: https://github.com/elastic/elasticsearch/issues/115600
 - class: org.elasticsearch.oldrepos.OldRepositoryAccessIT
   method: testOldRepoAccess
   issue: https://github.com/elastic/elasticsearch/issues/115631

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/cluster.stats/30_ccs_stats.yml

@@ -70,6 +70,7 @@
           body:
               settings:
                   number_of_replicas: 0
+                  store.stats_refresh_interval: 0ms
 
   - do:
       index:
@@ -79,6 +80,10 @@
         body:
           foo: bar
 
+  - do:
+      indices.flush:
+        index: test
+
   - do:
       cluster.health:
           wait_for_status: green