Fix CCS stats test (#115801) (#115965)

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

Fixes #115600

(cherry picked from commit 5f4e681788347969b71c8948df849cf12ea3f5d0)

# Conflicts:
#	muted-tests.yml

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